If you're competent with something you should move on. If you aren’t feeling discomfort and uncertainty with what you're doing, then most likely you should be doing something more difficult. Competence is nice, but a scary place to sit. You are capable of more than that. You should always be moving forward, and if you stop too long to enjoy competence, then you stop growing. On the other hand, discomfort and unfamiliarity is where you grow the most. You should (within reason) seek out that feeling of discomfort because it is stretching you.
And when you are stretched; when you do more than you’ve ever done, and better than you’ve ever done, thats where you will feel achievement and success