What event(s) in your life matured you considerably in one fell swoop?

I guess sometime in your life, you must have been pretty immature.

Then there had to be a significant event or two that made you grow up FAST. I mean, quite a bit faster than you would have otherwise.

What were those events, and how did they mature you in a hurry?

(I know of one example from the numerous documentaries I’ve seen: Basic Training in any military branch can really do a lot to one’s mind and emotions. If you have gone through BMT, please tell us how that has matured you.)