"If you've never seen it happen and don't know how it could happen, on what do you base the idea that people can change their own sexual orientation? And again, why can only some people do it?"
@ShodanLives, if you read earlier through this thread you will see I initially started out with the question of whether sexuality is unchangeable or whether it develops and changes over a life time. The idea is not that people can change it is that it is possible that they might be able to. That this exists as a possibility.
Reasons why I think it might be possible is that on a macro level (i.e within the same sexual orientation) what is found to be sexually attractive can definitely change. And on a societal level this changes too. I also remember vaguely at approximately 5 years old being outraged women couldn't marry other women. I wasn't that impressed with men or boys at the time. However, as I grew older I found I was straight and didn't particularly fancy other women. All my teenage crushes were male, I had boyfriends then married a man.
Why some people and not others? I really think a lot depends on what a person thinks is possible, their motivations and what they want out of life. I know generally ideas over what is possible affects the things I aim towards, plus I have to want it and be motivated.
"I don't define my own sexuality any more than I define my eye colour. It just is. And I'm not sure I ever really believed I could change my own sexuality, it was pure desperation on my part. Desperation born of what I faced from people like @HandyLady, whose vile video is what I was responding to in the first place."
And I haven't placed any value judgement on that. So you didn't believe you could and the motivation stemmed from other people's prejudice and criticism. So it sounds like this wasn't something you personally actually wanted or thought was desirable.
Personally, I often find possibilities and uncertainties quite empowering. And if I want things to remain as they are I can feel satisfied that is because they have value to me.
I wish you well, @ShodanLives.