It absolutely makes sense to make your fallbacks independent from one another, but implementing fallbacks at all is expensive. In evolution, you're pretty much

It absolutely makes sense to make your fallbacks independent from one another, but implementing fallbacks at all is expensive. In evolution, you're pretty much guaranteed a breakage at some point that can't be fixed. That's not quite as true with software - you're still guaranteed breakages, but you get to fix them, and fixing dependent systems is a whole lot more economical. I think the best analogy is interfaces. You code to an interface with multiple implementations, and if a problem occurs, you switch implementations. Next, if you have vulnerable and complex components, you make sure they each have a custom implementation, so the inevitable bugs can't be widely exploited.