Why do people complain, I want answers from everyone, it's for science fair, I just need to know why you as a person feel the need to complain?

I watched this video once by Drew Gooden. It was about why people get so mad nowadays. He basically makes a point on how our little 'cavemen' brains still need to be angry like its one of our needs. Sometimes it feels good to be angry even without a reason. I feel like complaining is a similar 'need'. Like when things get to big for our minds to handle and we just let it into the world. Almost liks a coming mechanism for stress or anger etc.

People has anger already and when they see this they feel even more annoyed and complain

Explanation:

I feel what you mean I really don't like it.

one day because their over eating or whenever it kicks in their body