Because you’ll always have a boss

When you start out, you have a boss.

When you’re promoted, you get to be a boss to other people, but you still have a boss yourself: you report up the chain of command.

When you’re promoted to CEO, you get to be a boss to a lot of other people, but you still have a boss yourself: you report to the board of directors.

Even after you quit and start working for yourself, you have a boss, but that boss is you.