It seems to me that one of the most difficult jobs for a software programmer is both keeping current with what languages are in demand and anticipating what languages are gaining in popularity.
For example, let's say you had a computer programmer that could make BASIC, PL/1 and assembly sing 30 years ago. How much would that programmer's skills be worth today? Probably not much, meaning that programmer would have to keep current with what languages were popular at any given time to stay relevant.
Also, let's say a programmer 30 years ago decided an emerging language such as Logo was going to be the next big thing, so he or she spent a lot of time learning it. Those would come across as wasted hours now.