Children react to things that they do not want to do with a pretty standard reaction. They push back on reasonable requests. Say no. Throw a fit. Or just plain ignore you and do what they want to do.
As they mature we help them see healthy ways to have these conversations. We help them see when they should do things they do not want to do. We help them convey their emotion in a healthy way. They start to develop their own ability to process their thoughts and feelings and convey them in a socially acceptable way.
Through the process, they become more mellow.
Their behavior changes when their parents call them out on unacceptable behavior.
How are you acting like a child (saying no, throwing a tantrum, ignoring requests)? How are you acting like a parent (calling others out when they act in unreasonable ways)?