The biggest downfall in my experience has been it can be a massive pain to find out where a method is defined in a huge codebase, especially with all the crazy ways in which one can declare methods. You can spend a non-trivial amount of time just trying to find the definition for a method.
Sorry if this sounds like a stupid question but - is there no "Go to definition" command in an IDE that can help with something like this? I mean, I understand that there is, but it doesn't work well with Ruby. Why?