When a mammal meets another mammal, each brain instantly decides whether or not it can dominate. Survival depends on it.
Why can't we all be equal, you say?
Equality is an abstraction you create with your cortex. Your mammal brain just wants to know if it can grab a piece of food without getting bitten by the mammal next to it. A mammal starves if it never goes for the food in front of it. But it if takes something a bigger critter has its eye on, it is quickly bitten or scratched. Painful experience teaches animals to make a submission gesture the instant they see a more dominant individual.
Of course we're not animals. But we've inherited the limbic system that mammals evolved to survive in groups. This limbic system controls the neurochemicals that make you feel good or bad. If you want to feel good, you have to make peace with your limbic system.
The mammal brain releases serotonin when it's in the one-up position because that promotes survival in the state of nature. The serotonin feels good, which motivates a mammal to seek the one-up position again.
Of course this sounds evil to modern sensibilities. So we learn to feel one-up in socially constructive ways, whether through public contributions or telling good jokes. But down below your sophisticated cortex is a mammal brain looking for something to feel superior about. Mammals have been doing this to survive for two hundred-million years, so I think some self-acceptance is in order instead of shame.
My book I, Mammal describes the evolutionary origins of our brain's urge to one-up our fellow mammal. No one like to imagine this in themselves, though it's easy to see in others. When you know how your neurochemical ups and downs are controlled by your mammal brain, you have more power over them. My book The Science of Positivity: Stop Negative Thought Patterns By Changing Your Brain Chemistry is a plan to feel good about life in a world full of mammals.