I recently read a very interesting essay entitled "The importance of stupidity in scientific research" and I wanted to share it with you. The author observes that feeling stupid is an essential aspect of research, because you are supposed to understand something that nobody currently does (as opposed to trying to solve a very difficult exercise). That might be why many very good PhD students feel discouraged, because they don't realize that feeling stupid means you are probably doing something valuable! Here is a quote that inspires me as a PhD supervisor:

We don't do a good enough job of teaching our students how to be productively stupid

Have fun!

Romain