Exactly this. I'd take this a step further and expand your knowledge with a sense of breadth too. Suppose you currently only know Java, it's far more useful to

Exactly this. I'd take this a step further and expand your knowledge with a sense of breadth too. Suppose you currently only know Java, it's far more useful to learn something completely different, e.g. Lisp/Clojure or Prolog than it would be to learn C#. The broader one's background the easier it is to pick up anything new along the way, and if there's one fact of life as a developer, there'll always be knew things to learn along the way.