How can anger stem from fear?

Which is then ultimately powerlessness.

I kinda realized that after a lot of years of incredible anger, trying to work it out and seeing it in others.

Powerless to change the world to make things better for yourself, to have the things you want, to make people like you or do what you want.

Watching extremely rich or famous people who seemingly have everything most of us might want become angry pricks because even then, they do not have ultimate power and they cannot control every fucking detail of the world around them.

As I said, Anger is a tool to attempt to claim or reclaim power. There are a lot of times when making that attempt is a really bad idea.