Learning one computer language is not enough. Knowledge of only one computer language or a few cripples the mind and causes the brain to run in circles. Different programming languages introduce different insights: various easier ways to do certain things, different restrictions , different syntax, different APIs, different ways of doing things, different high-level mechanisms (or lack of them). All of this gives different understandings of how to program in any language.

Many people believe that their limited knowledge is adequate. Java programmers are especially notorious for being opposed to the ideas of them having to learn different languages. The Pragmatic Programmer book says a programmer should learn a new computer language at least every year, and I tend to agree with it. I compiled a tentative list of the technologies I found the most enlightening, and I recommend programmers to learn at least all of them.