This is where luck comes in. If you wait until something is super popular then you lose the advantage of being one of the first people that understand the technology when it goes into production. Also sometimes you may learn something that never pays off but later it feeds into something that does. I spent a lot of time learning Common Lisp and could never apply that knowledge at work until functional programming became more mainstream and Scala&#x2F;Clojure became acceptable languages for production.