Probably my childhood. My parents divorced when I was ~4, and my brother and I began to live with our mother, and see out father every other weekend/holidays. During that period it was a fairly normal childhood, we'd play outside, get good grades, whatever sans a whole family. My dad remarried within a year. This woman wasn't a step-mom, more of an anti-mom. She had 3 kids a few years older than us, they'd bully us, throw me out of the bathroom, take my Christmas presents. I'd be too scared to leave my bed at night to use the restroom I'd just sit there and go, and then be punished for it. My brother and I were more or less neglected/abused at this place. This woman asked my dad to favor her kids more than his own, and not only did he do nothing, he went along with it.
Later, our mother moved us across state to a very poor area, we were likely among the poorest in town. But, we had fun, made new friends, did ok in school. Then drugs started to become into the picture. My mother dated some scumbags who were into coke. One night she came home with a black eye. Another night, this boyfriend was at her sisters (sex or drugs I assume), and my mom knocked his ass down (proud of that). This sister was actively involved in drugs and always owed people money - someone blew up her car as retaliation. My uncle wasn't very happy about this and gave her a black eye, to defend her sister my mother also received a black eye. I was crying at school the next day.
Later, we moved back across state to live with our dad. At this point, my view of myself and of the world was completely fucked, I had seen a lot of pain. At the new schools I found it hard to make friends or even talk to people. I began to loathe school, I didn't feel good enough to fit in. My grades dropped, eventually I slowly stopped going to high school in general. I dropped out, I still don't tell anyone that.
I found solace in gaming, there there was success. I made friends, became great at it, joined the best teams, eventually became a professional (it's a thing). On the other side, my non-digital life was next to non-existent. My dad would punish this behavior instead of understanding his children, any child is going to latch onto success and happiness. As I only saw him weekends as a kid he was never really involved in my development or active at key life events.
I eventually got a job and had girlfriends, and things were ok. But I wasn't doing much professionally to begin a career. All of my self-value was placed in these relationships and when those were gone, I was a mess. My last ex-girlfriend was my buddies girlfriend. I slept with her on a drunken night, and while I told her to stay with him it became a thing. We eventually became lovers, and this friend wished death upon me. I also worked with him, his mother, and his grandma - he was a favorite at work (so was I, but not so much after this). Work was miserable from that point on. The relationship failed - trust issues, and again I was left with nothing. I've spent the last ~4 years alone for 85% of the time I'd estimate. I'm a relatively social person, and not many would guess this is my life - even what few friends I have.
To this day I find it hard to imagine a future without pain, build relationships, trust anyone - including myself, or even handle basic skills like paying bills or waking up on time. I've began to make positive changes, but it's slow - and your environment can completely fuck up how you view yourself and the world.