Birth for a starter. I wasn't raised in a religious home, but we knew we were Jewish. I could have turned away into an American universalist. In my childhood days, most people had religion, except for the rare intermarried family.
Today no religion is more common.
I'm the type who likes to be part of something, and if I'm part of something I take it seriously. So, today I'm a Torah Jew, aka Orthodox.
It's a good question, and I'm sorry that I don't have the time and energy at the moment to give it a better answer.