If you “accidentally” got pregnant, how did it ACTUALLY happen? Did he accidentally come inside you, pull out too late without you realizing it, or was it from “pre-cum”??

I have wondered this forever bc I don’t really understand how it’s an accident or surprise if he HAS to come inside you, or if it actually does happen from pre-cum. I’ve read from different sources everything from it’s completely sterile to high chance of pregnancy. What is your experience??

Ps. I’m not worried or anything I just really want answers 😂😂