There was a story about a girl that would sneak up behind her younger brother while he was 'wanking' and pulled her underwear over his head when he was about to climax. In the story she was relaying this to a friend, saying he can now never get off unless he has ladies underwear over his head.
I have often thought that something is done to us, like rectal temperature on a regular basis, and it is either embarrassing or no big deal.
BUT, one day that very same mundane (or not) situation occurs just when our bodies and mind align with puberty and or sexual excitement, or erection for young men. One day it is just different. Emotional.
The curse of knowing.
True story, one day my stepson, myself and husband were watching a movie. A funny line was spoken in the movie that was a double entendre. He turned around, and at that very moment, his eyes got really, really big and said, "You two are laughing at something very different than what I was laughing at, and it happens a lot!"
For me it was quite phenomenal to actually see the change in him, not only did he get the dirty joke, he realized and was quite correct about it happening a lot and that he was forever changed. Of course the change was going on in his body gradually, but my thought is, it literally happened in a split second. And believe that is what happens to us with fetishes, or other sexual kinks and coupled with some emotion.
@Turkey1 aka LadyM