The day you think you have nothing more to learn you should stop flying - because you are either:
1. Perfect, so you might as well retire at the top of your game rather than risk going downhill.
or...
2. Complacent, and therefore a liability!
There's always something you can improve on. Don't just acknowledge mistakes though - develop a plan, strategy, check-list or procedure that will help you to eliminate them from your next trip. If you make the same mistakes twice - shame on you.
Acknowledge your successes too - and, as above, figure out what contributed to the good sorties, or aspects of it, so that you can repeat that success reliably.