"Some" of any group are morons. When I was coming out, uniformly the response from mature members of the LGBT community was that defining myself was not useful

"Some" of any group are morons. When I was coming out, uniformly the response from mature members of the LGBT community was that defining myself was not useful, and that it wasn't important to stress out over whether I self identified as straight, bisexual, gay, queer, or whatever. What's important is that you're happy, that you're not preventing yourself from forming romantic and sexual relationships with people you want to do so with, and that you're not facing discrimination for those relationships. I've personally had probably a dozen friends who thought they might be bisexual later decide that they were straight (and many who decided they weren't). I applauded them for their open mindedness in seriously considering it, and experimenting to see the truth of the matter (we were all scientists and engineers, after all). After that process, I am certainly more confident that they are actually straight than if they'd just assumed it to be the case without evidence. So yeah, in my experience people are "born gay" "born straight" or "born flexible". Some people "born straight" experiment with bisexuality, and end up the better for it. Some people "born gay" experiment with heterosexuality, and end up the better for it. And unlike some, I do believe in bisexuality, or being attracted to someone based on personality alone. It's much more rare than a fixed sexuality, but I've definitely met people who very legitimately are interested in both men and women.