Very few, I do acknowledge that bad things happen, but you grow from them. However, sometimes that growth isn't worth the priced paid.
One situation was when I was around 7 or so, I had just skipped a grade. I received lots of praise at school and even from my often belligerent mom. Everything was great, I was on Cloud 9 and I thought the absolute world of myself, a wild swing from what I was before. One day while I was walking home I noticed 2 men in a vehicle following me very closely, I still remember the fixation in their eyes. I was smart enough to recognize the threat and I figured "these guys are waiting for me to get into an isolated place." So I did the very thing they wanted, I -pretended- to walk down the steps to an underground parkade. As soon as I did this they hit the gas and raced down to greet me. That confirmed my original suspicion of what was happening and I spied on them for a bit before I left. As I walked away I patted myself on the back thinking I was brilliant, someone at my age easily outsmarting 2 much older guys. Ha, I felt like the kid on Home Alone. The problem? I never told anyone about it and later that day a nearby local girl was abducted.
While I never actually knew the girl, I gathered all my friends and constantly went around town asking around and looking for her. It made the news (naturally) and cops were filtering throughout the city looking as well. Since my mom was a single nurse, she often worked at night. I was gone for about 3 days or so, all night, constantly looking while I rode around on my bike. The types of people I spoke to, the places I went... all shady areas and I could have easily just been another casualty.
I never found out what happened to that girl, but I never forget it either. I learned a lot through that experience and specifically learned to never let myself get carried away with my own hubris. I also think it was one of my greatest inspirations to go into policing.
In the end, while I weathered most of that immense level of mental turmoil, I ultimately gained so much more strength from it in return. With that said, I would give up everything I am today, even cease to exist, if that girl would have never went through that experience.