Some of it was open contrarianism. No wedding, no kids, no car, all on principle. This was a way to refuse to live by someone else's script. I/we didn't need these things, so I/we opted out.

Some of it was fear of despair. My mom died a wage slave of a heart attack on the job. I was not going to let that happen to me, so I learned about personal finance and learned about refusing to live by the standard script of buying what I couldn't afford, keeping up with the Joneses, and so on. This also meant leaving the big city. It also informed the decisions about wedding, kids, and car.

Some of it was metta meditation. As I learned to have compassion for others, I learned to see their expectations of me as regrets about themselves. This made it easier to consciously ignore them.

Ultimately I learned to pay attention to every time I thought about what I "should" or "ought to do" and challenged myself to find a reason to do that thing that felt genuine to me. Did I really need to? What bad thing would happen if I didn't? Would I truly value it? And when this led me to find no genuine, compelling reason, I didn't do it. I became allergic, in a sense, to "because I'm supposed to".

I'm not sure whether that actually explains anything, but it's what I can offer for now. Further questions are welcome.