Ten or something years ago, I was determined to become a professional (or at least a winning) poker player. Poker bores me now, but there's a few things I learned back then that have stuck with me.
One of them is to not be outcome-determinative. This means that you can't judge your decisions based solely on the outcome. This is critical for a professional poker player who must be willing to ride the ups and downs of the cards. Even the greatest poker pros in the world have sessions where they lose money. And it's really tempting to change up their gameplan based on one session, (e.g., "Aw, crap, I shouldn't have folded. Next time I won't.") Instead, they have to be confident they made the right decision with the information they had at the time, and that making such a decision will win them chips in the long run.
Sometimes it is better not to learn from our mistakes... because it might not have been a mistake in the first place, regardless of the outcome.