There's of course numerous I could mention, but one seemingly understated one from the outside, one that no one else was present for, sticks out to me in this moment. I dealt with depression as a teenager, and there are chunks of memories in my mind with a dull gray filter over them because of how apathetic and nihilistic I felt at the time, just going through the motions of life. It was a feeling I didn't want around, but I couldn't shake it, I couldn't help but feel beholden to it for some unknown reason. When the feeling persisted in college and was affecting what I had been told were supposed to be the "best years of my life", it was bringing me down even more.
I can't explain what really caused the turn around moment. There's no big revelatory lead up or symbolic moment. But I just suddenly realized, when I was either 19 or 20, that my mental perspective was in my control. That sure, nothing mattered, but it could matter if I chose to make it matter. And no one could help me out of my depression but me (because by that point I knew, many people had tried), so by the strength of my will, I would choose to be a happier, more positive person. I would choose to create meaning for myself because I want to.
It's funny because other people had definitely told me about how powerful perspective can be, but I couldn't internalize it. I also recognize that depression is not just a matter of lacking willpower; that it indeed is a chemical imbalance in the brain. And I think the moment for me was probably due to a combination of my body coming out of the teenage hormone phase, and me doing a lot of introspection about my mental state at the time. But, it's made a big difference for my life ever since.