We do learn from people, like you mentioned both good and bad. It is what we do with the lessons that build us as a person. Your friend took the good lessons, learned and grew, he also learned how to stop and think! That is one part that people have a hard time doing, when the emotions are running it is very hard to stop and think what we are saying.

Some times you have to let go, but then you need to know when enough is enough when letting go. It is bad to keep it bottled up, but just as bad to let it run and run and run, and have no idea of when to just stop and think. I run into the rant part of life on occasion, and have a difficult time sometimes to just let it go.