Why People Blush In Pleasure

First of all, it's not everybody that blushes in pleasure. In fact, it's only a small minority not exceeding 20% of the general population. But why do they? Why would anyone? And who are they?

They are sun-worshipers, the personality defined by raising the minimum for everyone around them. And they blush in pleasure because pleasure is associated with personal good fortune. And because blushing happens due to embarrassment, and embarrassment is caused by violation of your personal values.

Since the sun-worshipers want to raise the minimum standard for everybody, any personal good fortune that falls upon them would far exceed the minimum standard and thus they're enjoying something which violates their values, thus causing embarrassment. This only kicks in if the good fortune is non-tradeable.

Thus, a sun-worshiper wouldn't feel embarrassed winning the lottery because they can always give it away to the poor. And they will do just that. But getting an excess of attention or an excess of sexual attraction would be embarrassing because there is no obvious way to hand it off to anyone else. They're stuck with enjoying it.