This lesson has presented itself many, many times. Never have I understood it so clearly as when my daughter confirmed it! It's not the pain she endured, but the people she hurt in the process. However, if it weren't for her experiences, she would not be who she is today. AND she says that she "Loves who she is".
Hindsight is 20/20. No regrets for making the mistake of allowing the toxicity back in my life because now I see clearly what to avoid and it'll never happen again. Life is too amazing to live in regret about past relationships.