Nicely expressed, and I agree that programming languages and frameworks aren't quite as mysterious as HR sometimes seems to think they are ("sorry, we need 5 ye

Nicely expressed, and I agree that programming languages and frameworks aren't quite as mysterious as HR sometimes seems to think they are ("sorry, we need 5 years with rails, not grails, so, you know, can't hire you… oh, and there's a terrible shortage, we are having tremendous trouble hiring"). That said, I do think that programming languages and frameworks are only about 10% of what makes a programmer "fungible." Here's the line that stuck with me: "Then you should just go ahead and hire the RoR person and give them a month or so to figure out the Django conventions and vice versa." I completely agree that a company may need to give at least a month over to pure study and investigation (wait and see what the stakeholders have to say about that, though - a very blunt discussion about reality may be in the cards here). Here's the thing - depending on the existing code base, familiarity with a new framework may be the least of your problems. If it takes a month to get used to django instead of rails, it can take several more to get used to the code base itself. So you're looking at a situation where a new programmer may not be highly productive for the first 5-6 months after hire. To me, this does stretch the notion of "fungibility." It means that if a programmer leaves a project, you may be looking at 6 months before any progress can be made - and that's assuming you can find a talented enough programmer to get up to speed in the first place (that can take 6 months). Often, a good previous developer will take copious notes, document well, ensure easy and clean build and test practices… that can reduce the ramp up time. But a lot of this is just building a very elaborate blueprint for a system in your head. Good practices can make it quicker and easier, but in the end, the transition just takes a lot of time. There are tasks that would take a programmer with full context 1 week to complete. Optimistically, it could take a new programmer 3 months + 1 week, and that's for a well prepared programmer who understands the existing tech stack or something closely related. Keep in mind there are are so many things about an organization to understand - existing database systems, services, security policies, auth systems. The amount of context you have to build up can be massive. Actually, that's not a bad way to measure fungibility. The ratio of how long it would take a current worker to complete a task vs a "well prepared" replacement. 1 week / 13 weeks ~ .077 fungibility.