I completely agree with this. In some cases focusing on a single language or set of languages can be a good idea - especially when it is a language in high dema

I completely agree with this. In some cases focusing on a single language or set of languages can be a good idea - especially when it is a language in high demand and it means you know the ins and outs of a lot of different frameworks a la javascript. However, there is no downside to studying a lot of different languages because it gives you general experiences that you can apply to other languages, it helps you pick up new languages and toolsets, etc. The most basic example is that a programmer who only works with imperative languages should dabble in at least one functional language, because that can change the way you view algorithms, data structures, and overall program layout.