Genetics and environment like GasMonkey said, and personality. Bad childhood/parents, never had friends or support, never fit in in school too quiet, traumatic event, lots of financial stress being on my own early on. But the final straw that has got me to the point where I am really serious about it is because of my mild social anxiety, or whatever it is that makes me not normal. I'm too quiet, bad at talking, don't fit in with most people. I've worked since high school and my current job is ok, but I am still very aware of how I am and how it has been such a theme in my life, that I am the issue, and there's nothing I can do about it. I guess these past few months this has really become apparent to me, I can't do it anymore. I want to live, but I can't do it like this, I am not built to function in society. I will always have more trouble fitting in in the world, and you need to fit in at work to survive and be happy. I'm on my own, so I'm not waiting till the point I'm homeless and have no way out especially as a woman I won't make it like that, I don't even see it as an option. I only have one parent that may let me stay with them if it came to that, but if it came to that I am not going to be well enough to go back and start all over again, and my parents for sure are not willing to take care of me financially. My reality is because of this it's not possible for me to live a normal, happy life. None of it has been so far either. I could continue and see what happens, but I know I can't handle anymore and can barely function to work at this point, just waiting until I can ctb.
People say ctb is a permanent solution for a temporary problem, that doesn't apply to my situation. If I choose to live I will end up homeless, or live a life of constant struggle, suffering and isolation. I've looked into it and it's pretty clear that the way I am is not something that ever goes away, even with therapy and medication, even with more exposure. I would have to keep struggling and coping, trying to be a tiny bit better my entire life, and I know I definitely cannot handle that on top of all the other stresses of life.