When you're having sex, something in you is increasing or rising, whether you call it passion, tension, or something else. For most men, this is either the penis or the scrotum. It's before this point is reached that you need to do something to control ejaculation. Men who have good control have learned that control, usually without knowing they learned anything. And all of us, whether we have ejaculatory control or not, have learned to control other reflexes.
Urination is perhaps the closest parallel.
At some point when you were very young, your parents let you know that it was no longer acceptable to urinate in your pants. You gradually learned to recognize the sensations in your body signaling that you were about to urinate, and you could tell someone that you had to get to a toilet. You could tell something was about to happen, but you couldn't delay its occurrence. As time went on, you completed your training. You not only knew when urination was imminent, but you could also exert some control to delay it.