Some technologies are not used by the vast majority of people (e.g: Erlang, Oz, Haskell, Prolog) but working with them will always offer you a valuable lesson i

Some technologies are not used by the vast majority of people (e.g: Erlang, Oz, Haskell, Prolog) but working with them will always offer you a valuable lesson if they teach a different paradigm. e.g: the actor model, dataflow concurrency, logic programming and so many more stuff. Those are extreme examples of different paradigms. So, the question now is: are you cultivating skills related to an obsolete paradigm, or a skill that you cannot trade in the market? If so, that's not good.