I read a career advice answer on Quora that was really amazing. This is the question and answer:
I really love the answer, but in particular the first two points. First, focus on constantly learning and pushing yourself is absolutely my tenet. Not only that, but remember that you're only competing with yourself - don't compare to others. Good things will happen if you keep learning and improving.
The second point in the answer above is about when to quit. I read The Dip: A Little Book That Teaches You When to Quit (and When to Stick) while on vacation last year and it does give us some good recommendations when to consider pursuing what you've been doing so far as opposed to when you should quit. In my opinion, given my professional experiences, I believe that people tend to keep pushing more than they should - and although I could speculate the reasons they don't quit, the point is just that they don't realize or decide not to quit early enough.