Just-In-Time learning means you learn a thing because you need to know it right then. Just-In-Case learning means you learn a thing because it may come in handy at some point in your life. This separation is already well documented, even on Wikipedia.
It gets more interesting when you combine it with expiring skills vs. permanent skills. Expiring skills will eventually stop being useful, and permanent skills will be just as useful decades from now as they are today. Permanent skills compound over time, and expiring skills don’t.
So if you learn an expiring skill, and don’t end up using it right away, then it’s only a matter of time until that skill is irrelevant, and all your time spent learning it was wasted. If you know a skill is going to eventually expire, then you should only learn it if you’re sure you can use it.
Expiring skills should only be learned Just-In-Time, but permanent skills are worthwhile to learn Just-In-Case.
But the tricky and somewhat disappointing bit is that the only skills we can consider permanent are soft skills – things like attitude, discipline, charisma. Hard skills like Typescript and Kubernetes will eventually be obsolete, so learning them Just-In-Case is a waste of time.
But then how can I ever become a well rounded technologist, you ask? You work really freaking hard to get on projects with technology you haven’t used before. If you get an opportunity to hop onto a project using some tech that’s new to you, then do it.
When someone asks for some help with a build system you’ve never used before, raise your hand. When a project needs realtime streaming data and you have no idea how to do it, raise your hand. When a client gets excited about creating an Alexa skill, raise your hand.
Raising your hand gets you the best of both worlds. You get to become a well rounded technologist and avoid wasting your time learning technology you won’t ever use.
So raise your hand to learn the hard skills when they’re needed, and spend your Just-In-Case learning on the stuff that will stick around. Put down the Python book (unless you’re working on a Python project) and pick up the book on habit forming, or dealing with difficult people, or taking ownership.
That’s the stuff that will compound for the rest of your life.