>people who regularly throw a party and people who never do it.

I have no doubt it might seem that way, but it doesn't seem like an interesting divide because the categorization doesn't really tell you anything about the people. But it's definitely a good rule of to thumb to remember the next time someone feels annoyed that "so and so never throws parties." It's also true when you visit friends in cities you never been. Some are natural and enthusiastic tour guides, some shun such a role.

But my guess is many the "never hosts" threw at least one party in the past and had a terrible experience and decided they suck at it.

I'm also assuming the never people you know are capable of throwing parties in terms of house size etc, and that you accounted for the ineligible in that respect.

I know people who are self-conscious about their messy houses and the idea of maintaining a presentable tidy house for parties would be enough for them to dismiss the idea outright even though they would like to do it in theory.