The first was having an abusive parent. I often used to wonder (as a child) how, and why, my mother put up with it. It wasn't until I was much older that I understood more about it. Then the abusive one died, and it was such a relief. Home was a much more relaxed, and happier, place. It made me realise how much of an influence one person can be over others, and the effect that we can have on other people- both positive and negative. Even as a child, I thought, "I'm never putting up with that as an adult". Thankfully, I don't, and my sibling seems to have broken the cycle of abuse by actually being nice to their child.
The second was having a nervous breakdown. It made my mother realise how bad things had become, but other family members still stuck to the, "mental health problems aren't real. There were people who came back from the war with less..." (yes, and one family member had to drink himself into a stupor every night, just to get to sleep). It made me realise how much pressure my family exerted on me, and it was very stressful. I don't remember much from that time, apart from lying there in bed, thinking, "I did what I was told (A-Levels, a degree and a Proper Job), and it didn't make me very happy. Perhaps I should try what I wanted to do in the first place, and see if that makes me happy"... so I did, and it worked (mostly). The breakdown also had the unintended, but very useful, consequence of encouraging me to say, "No" to things that would be too stressful for me to cope with. I've been told that I'm selfish for not giving in and the likes, but my mother has told me at times that she feels the same way... so it gave me more motivation to get sufficiently far away from the village where I grew up, and my family, to experience the non-stop novelties of privacy and independence.
It also made me less anxious, and realise that I don't want to be sat in an old people's home, thinking, "I wish that I'd done X, Y and Z when I had the chance". I have one shot at life, and it's my job to make it as happy and interesting as it can be, for as long as I'm on this earth... so perhaps that nervous breakdown was a blessing in disguise, for giving me the courage that I didn't know that I had.