Very true. To me, categorizing skills on the dimension of expiring vs non-expiring seems to be implying the latter has greater value than the former. This isn't

Very true. To me, categorizing skills on the dimension of expiring vs non-expiring seems to be implying the latter has greater value than the former. This isn't true in all situations. Foundational skills are just that -- foundational, in that they are a base to build upon. The stronger your foundation, the stronger your base on which other skills are attached. That said, the base itself it rarely enough. I'm sure we've met people who've mastered the foundations but have never done anything interesting in their lives. I have friends who were super good at calculus and linear algebra (the foundations for engineering math) in college but never amounted to much in their careers. On the other hand, it is sometimes in acquiring so-called expiring skills that we begin to see patterns of the foundations skills that would be useful. Thoughtful programmers without CS degrees -- who have written code for years -- often find SICP a revelation that validates or corroborates their experience in the real world. On the other hand a college instructor who's taught SICP for years and can recite it from memory may never know how to apply it because he/she has never learn the "expiring" skills necessary to execute in the real world. Some people change the world on so-called "expiring skills" -- because even though they are only useful for a season, they might be very high leverage during that season, and it gets you into the game. Once you're inside you can pivot. I knew a bunch of folks (with no prior programming backgrounds) who got their start from PHP (an expiring skill) and are doing well today. I cut my teeth real-world programming with Perl (arguably a expiring skill). It was very much non-foundational (I would never do things today the way I did them in Perl) but it was my foray into real-life programming and it got me gigs. I wouldn't have gotten into programming if I had studied programming via a foundational CS curriculum.