It is a really good question. I struggle with it every day.

To me it seems like popular people go along to get along. They never offer resistance. They do what other people want... pretty much always. They never take offense at anything and never noticed that they are treated different. Sort of like a dog.

To the extent that you do look out for yourself or do what you want or offer any resistance... you are not liked.

At one point I read something that I am not sure about, essentially it says that the bacteria in our gut is unique and if your bacteria poses a threat to someone else's bacteria... the bacteria tells your brain to get away. Maybe what they mean by a "gut feeling"