@calm That depends on the nature of the mistake! If it's a skill-based mistake, then as many times as it takes you to gather the necessary experience before you stop making the mistake.
If it's a mistake based on non-skill based decisions, such as breaking rules to your benefit, or cheating on someone, then exactly once. After the first time then you're just taking advantage of other people's forgiveness and are a dick.
It shouldn't take more than once to understand how your actions affect those around you. If you're just going to apologize over and over, then you're not learning anything and it gives the impression of being insincere.