7 ms·

The Broken Chain Problem

111 points by headalgorithm 7y ago

andi1304 7y ago
"When you want to influence the world around you, make sure that your action is causally connected to whatever you want to influence." How can we know when an action is causally connected to an effect? Western philosophy since David Hume has struggled to find a solution to this problem. The 'problem of causality' is that it is extremely difficult to establish cause and effect with any degree of certainty. All we have is correlation. Modern thinkers (e.g. Judea Pearl) are still grappling with this problem today. Pearl's fascinating talk on this subject at PyData 2018 is available on YouTube: https://www.youtube.com/watch?v=ZaPV1OSEpHw https://www.youtube.com/watch?v=ZaPV1OSEpHw
- twic 7y ago
  It only seems to be difficult for philosophers.
  - earthboundkid 7y ago
    Like many philosophical problems, regular people solve the problem of causality by plugging up their ears and saying "lalala, I'm not listening." And then we get crap like analytics marketing teams.
Gusmann 7y ago
Sometimes it's hard to identify a broken chain on the spot and a lot of marketing tricks are based on that. Highly recommend you to read Freakonomics if you haven't yet. Also this article mentions two observations of Richard Feynmann and I just can't stop admiring the curiosity and wit of the man. His biography totally inspired me and made me laugh a lot
yalooze 7y ago
I immediately thought of 2 related points: The Scream Test: If you see something and you don't know what it does, remove it and see if anyone screams. Chesterton's Fence [0]: "reforms should not be made until the reasoning behind the existing state of affairs is understood" (Though the purpose of this fence is not obvious, there may be valid reasons for its presence.) [0] https://en.wikipedia.org/wiki/Wikipedia:Chesterton%27s_fence https://en.wikipedia.org/wiki/Wikipedia:Chesterton%27s_fence
- kuu 7y ago
  Uhm, it's interesting, I see a little contradiction in your two points...
  - dagw 7y ago
    The person doing the screaming in option one would probably very much prefer you using option two. Option one assumes that you can easily reverse your action with no damage done, which very often isn't the case
  - coldtea 7y ago
    Well, it's about balance. If you applied the "Scream" test for a component you don't know what it does in an airplane, it might fall/explode/whatever. If you do it in a non-critical codebase, it might just break the build, and have someone call you for it. In the first case, the Chesterton's fence caution is more advisable. In the second, you could go with a "remove it and see what happens" approach.
    - jchanimal 7y ago
      There were a few times in the development of Apache CouchDB where whole features were “accidentally“ removed as a way of pointing out that the test suite didn’t exercise them.
  - yjftsjthsd-h 7y ago
    I would interpret them at saying, "if you don't know why something is there, break it", and "if you don't know why something is there, don't break it"; how are you interpreting them, then?
  - yalooze 7y ago
    Yes, that's deliberate. As others have said it depends on the context and the ease of reversibility / consequence if it's still in use. I see them as complementary. If the risk is low it may be simpler/quicker/more cost effective to turn it off and see if anyone screams. So long as you are listening for the scream and can easily turn it back on. Obviously this can be abused but there are times when it is useful. If the risk is high, definitely spend the time to understand why, even if it is non-obvious.
amelius 7y ago
Meh. If you take the average of everybody's nose length, you still have a better estimate than just pulling a number from thin air. Also, the inhabitants' action is basically what scientists do all the time when they run experiments. Correlation is not causation, but quite often it is a good lead.
- yosamino 7y ago
  They didn't average the length of everyone's nose. They averaged everyone's estimate of the emperor's nose.
- NoodleIncident 7y ago
  More importantly, it sounds like everyone who's going to actually see the statue got a chance to provide their input. So this method maximizes the number of people happy with that part of the sculpture, anyway!
hyperman1 7y ago
3 of these stories are on HN regularly, but the soviet one was new to me. Now I wonder: what should the central planners give as metrics? Is there anything that works?
- hoseja 7y ago
  Obviously, number or weight of standard-compliant nails.
  - dagw 7y ago
    But then you need someone to test the nails for standard-compliance, and what metrics should you give them to make sure they do a good job...
    - subroutine 7y ago
      You can revert to a count-based performance target, and test for compliance based on parcel weight (e.g. a 2-inch finishing nail weighs 0.79 g; if a factory reports 1 mil units, take a random .8 kg sample, check if there's ~1k nails).
      - dagw 7y ago
        Then the factory will just prioritize making sure all their nails weigh the same over any other consideration.
        subroutine 7y ago
        They should be prioritizing count (I mentioned that was the performance metric). They actually wouldn't need to "make sure all their nails weigh the same", only that on average they weigh as much as the template. If you can't save time by using less material, and you can't save time by generating fewer units, might as well make the foundry mold match the template, no?
    - peteradio 7y ago
jiggawatts 7y ago
You see this in every field, including IT of course. My favourite example of this was the introduction of the Microsoft Distributed File System (DFS) service into a customer environment. We were only using the DFS Namespaces feature, which is like DNS for file shares: the client downloads a blob of metadata and uses it to find an underlying file share for a logical name. The caching is very effective and the additional delay is negligible. They had a file performance problem. So of course, they point the finger at the last thing that has changed in the environment: DFS! It must be DFS! I calmly point out that if the performance is bad after a connection has been made, it can't possibly be DFS, it's out of path after the initial negotiation. It's like blaming DNS for slow downloads. Makes no sense! But nope. They just won't accept that. It's the last thing that has changed! I came back a week later to discover that instead of 2 redundant DFS servers, there are now 6 redundant DFS servers "for performance". To their surprise however, the file shares are still mysteriously behaving poorly. They dragged me along to a meeting with a cast of thousands to discuss the issues. One guy spent most of the time arguing for increasing the number of DFS servers to 8, 10, or perhaps even more to solve the issue! Meanwhile I'm having a side-conversation with the storage guy, who sheepishly admits that 3 out of 4 fibre channel paths were down, and this started at about the same time frame as the deployment of DFS. I point this fact out to the room. Everyone looks at me while blinking slowly. A few more moments of silence pass. Then someone helpfully suggests adding more CPU and RAM to the DFS servers. Maybe 8 processors and 64 GB will do the trick!
- selestify 7y ago
  I don't understand, why do things like this happen? Is someone emotionally invested in upgrading the DFS servers?
  - jtbayly 7y ago
    They are invested in going down the wrong path. They are invested in not being wrong.
  - jiggawatts 7y ago
    In this particular case it was "politics" in the smallest sense of the word. The head of the storage team did not get along with the head of the infra team, so the infra guys would solve the problems they could solve, ignoring any storage subsystem problems because that was a "dead end". This is exactly like the boy looking for the coin under the light. It feels like it could be productive, versus definitely not being productive. It doesn't matter that logically it won't work, it's the feeling that matters.
nwsm 7y ago
I look forward to analyzing the sequence of physical forces that connect me wanting to tell someone something to keys being pressed on a keyboard to an email showing up in their inbox as part of my decision process at work. We don't have time to analyze entire chains so we make assumptions about chains that should be unbroken. Occasionally but inevitably we make wrong assumptions.
jancsika 7y ago
> but none of the townspeople know anything at all about the emperor’s nose, so the causal chain from the actual emperor’s nose to the elders’ estimate is broken. They do. They are humans, and humans have noses. Using the statistical method decreases the chance that a wild guess by the sculptor ends up angering the Emperor and causing deaths in the village.
- sudhirj 7y ago
  I don’t think the sculptor was planning to sculpt an outlandish alien nose. The problem is that if your statue doesn’t look right heads will roll. The story isn’t about the selection of outlier data points as being representative - its more about drawing conclusions through seemingly plausible sounding methods that are nevertheless completely disjoint from the thing you’re reasoning about.

111 points by headalgorithm 7y ago

"When you want to influence the world around you, make sure that your action is causally connected to whatever you want to influence." How can we know when an action is causally connected to an effect? Western philosophy since David Hume has struggled to find a solution to this problem. The 'problem of causality' is that it is extremely difficult to establish cause and effect with any degree of certainty. All we have is correlation. Modern thinkers (e.g. Judea Pearl) are still grappling with this problem today. Pearl's fascinating talk on this subject at PyData 2018 is available on YouTube: https://www.youtube.com/watch?v=ZaPV1OSEpHw https://www.youtube.com/watch?v=ZaPV1OSEpHw

twic 7y ago
It only seems to be difficult for philosophers.
- earthboundkid 7y ago
  Like many philosophical problems, regular people solve the problem of causality by plugging up their ears and saying "lalala, I'm not listening." And then we get crap like analytics marketing teams.

Gusmann 7y ago

Sometimes it's hard to identify a broken chain on the spot and a lot of marketing tricks are based on that. Highly recommend you to read Freakonomics if you haven't yet. Also this article mentions two observations of Richard Feynmann and I just can't stop admiring the curiosity and wit of the man. His biography totally inspired me and made me laugh a lot

yalooze 7y ago

I immediately thought of 2 related points: The Scream Test: If you see something and you don't know what it does, remove it and see if anyone screams. Chesterton's Fence [0]: "reforms should not be made until the reasoning behind the existing state of affairs is understood" (Though the purpose of this fence is not obvious, there may be valid reasons for its presence.) [0] https://en.wikipedia.org/wiki/Wikipedia:Chesterton%27s_fence https://en.wikipedia.org/wiki/Wikipedia:Chesterton%27s_fence

kuu 7y ago
Uhm, it's interesting, I see a little contradiction in your two points...
- dagw 7y ago
  The person doing the screaming in option one would probably very much prefer you using option two. Option one assumes that you can easily reverse your action with no damage done, which very often isn't the case
- coldtea 7y ago
  Well, it's about balance. If you applied the "Scream" test for a component you don't know what it does in an airplane, it might fall/explode/whatever. If you do it in a non-critical codebase, it might just break the build, and have someone call you for it. In the first case, the Chesterton's fence caution is more advisable. In the second, you could go with a "remove it and see what happens" approach.
  - jchanimal 7y ago
    There were a few times in the development of Apache CouchDB where whole features were “accidentally“ removed as a way of pointing out that the test suite didn’t exercise them.
- yjftsjthsd-h 7y ago
  I would interpret them at saying, "if you don't know why something is there, break it", and "if you don't know why something is there, don't break it"; how are you interpreting them, then?
- yalooze 7y ago
  Yes, that's deliberate. As others have said it depends on the context and the ease of reversibility / consequence if it's still in use. I see them as complementary. If the risk is low it may be simpler/quicker/more cost effective to turn it off and see if anyone screams. So long as you are listening for the scream and can easily turn it back on. Obviously this can be abused but there are times when it is useful. If the risk is high, definitely spend the time to understand why, even if it is non-obvious.

amelius 7y ago

Meh. If you take the average of everybody's nose length, you still have a better estimate than just pulling a number from thin air. Also, the inhabitants' action is basically what scientists do all the time when they run experiments. Correlation is not causation, but quite often it is a good lead.

yosamino 7y ago
They didn't average the length of everyone's nose. They averaged everyone's estimate of the emperor's nose.
NoodleIncident 7y ago
More importantly, it sounds like everyone who's going to actually see the statue got a chance to provide their input. So this method maximizes the number of people happy with that part of the sculpture, anyway!

hyperman1 7y ago

3 of these stories are on HN regularly, but the soviet one was new to me. Now I wonder: what should the central planners give as metrics? Is there anything that works?

hoseja 7y ago
Obviously, number or weight of standard-compliant nails.
- dagw 7y ago
  But then you need someone to test the nails for standard-compliance, and what metrics should you give them to make sure they do a good job...
  - subroutine 7y ago
    You can revert to a count-based performance target, and test for compliance based on parcel weight (e.g. a 2-inch finishing nail weighs 0.79 g; if a factory reports 1 mil units, take a random .8 kg sample, check if there's ~1k nails).
    - dagw 7y ago
      Then the factory will just prioritize making sure all their nails weigh the same over any other consideration.
      - subroutine 7y ago
        They should be prioritizing count (I mentioned that was the performance metric). They actually wouldn't need to "make sure all their nails weigh the same", only that on average they weigh as much as the template. If you can't save time by using less material, and you can't save time by generating fewer units, might as well make the foundry mold match the template, no?
  - peteradio 7y ago

jiggawatts 7y ago

You see this in every field, including IT of course. My favourite example of this was the introduction of the Microsoft Distributed File System (DFS) service into a customer environment. We were only using the DFS Namespaces feature, which is like DNS for file shares: the client downloads a blob of metadata and uses it to find an underlying file share for a logical name. The caching is very effective and the additional delay is negligible. They had a file performance problem. So of course, they point the finger at the last thing that has changed in the environment: DFS! It must be DFS! I calmly point out that if the performance is bad after a connection has been made, it can't possibly be DFS, it's out of path after the initial negotiation. It's like blaming DNS for slow downloads. Makes no sense! But nope. They just won't accept that. It's the last thing that has changed! I came back a week later to discover that instead of 2 redundant DFS servers, there are now 6 redundant DFS servers "for performance". To their surprise however, the file shares are still mysteriously behaving poorly. They dragged me along to a meeting with a cast of thousands to discuss the issues. One guy spent most of the time arguing for increasing the number of DFS servers to 8, 10, or perhaps even more to solve the issue! Meanwhile I'm having a side-conversation with the storage guy, who sheepishly admits that 3 out of 4 fibre channel paths were down, and this started at about the same time frame as the deployment of DFS. I point this fact out to the room. Everyone looks at me while blinking slowly. A few more moments of silence pass. Then someone helpfully suggests adding more CPU and RAM to the DFS servers. Maybe 8 processors and 64 GB will do the trick!

selestify 7y ago
I don't understand, why do things like this happen? Is someone emotionally invested in upgrading the DFS servers?
- jtbayly 7y ago
  They are invested in going down the wrong path. They are invested in not being wrong.
- jiggawatts 7y ago
  In this particular case it was "politics" in the smallest sense of the word. The head of the storage team did not get along with the head of the infra team, so the infra guys would solve the problems they could solve, ignoring any storage subsystem problems because that was a "dead end". This is exactly like the boy looking for the coin under the light. It feels like it could be productive, versus definitely not being productive. It doesn't matter that logically it won't work, it's the feeling that matters.

nwsm 7y ago

I look forward to analyzing the sequence of physical forces that connect me wanting to tell someone something to keys being pressed on a keyboard to an email showing up in their inbox as part of my decision process at work. We don't have time to analyze entire chains so we make assumptions about chains that should be unbroken. Occasionally but inevitably we make wrong assumptions.

jancsika 7y ago

> but none of the townspeople know anything at all about the emperor’s nose, so the causal chain from the actual emperor’s nose to the elders’ estimate is broken. They do. They are humans, and humans have noses. Using the statistical method decreases the chance that a wild guess by the sculptor ends up angering the Emperor and causing deaths in the village.

sudhirj 7y ago
I don’t think the sculptor was planning to sculpt an outlandish alien nose. The problem is that if your statue doesn’t look right heads will roll. The story isn’t about the selection of outlier data points as being representative - its more about drawing conclusions through seemingly plausible sounding methods that are nevertheless completely disjoint from the thing you’re reasoning about.