We humans are far from perfect and we know it, too. Yet, we can be our own worst critics when it comes to recognizing how we made a mistake or error of judgment. We chastise ourselves for not being more aware or 'tuned in' to something we should have seen in an obvious way. Mistakes and errors of judgment can be wonderful things, though. Without them we don't learn and grow as individuals. That's why you needn't regret or resent having made a certain mistake now.
... or select your birth sign