There will be times when you have a difference of opinion. The person who specifically and explicitly has control has, indeed, got control. It's the other person's job to try to convince them. Working together well means taking the time to listen to concerns, then making a decision. Sometimes that means changing your mind. This is not a competition between you. Changing your mind or not changing your mind is neither victory nor loss.

But for every decision, someone should have control, and their job, in part, is to keep the other person informed. That feeds back to point (b) above.