To overcome sorrow about past mistakes ...

Look at the bright side, and look forward to the future. It's quite possible that the lesson has found you a better version of yourself.

Learn the lesson, pay your dues.
  1. At best, you now understand the problem down to its roots. It can't trouble you any more!!
  2. As the next best, you can turn the problem into an opportunity.
  3. At the very least, you've learned to avoid similar things in future.
Without these mistakes, you get the worst outcome: Like those who don't know History, you will repeat them indefinitely.