The fact that you call them "mistakes" proves that they are something which you feel are ugly and want to forget.
But the point is that they will forever be seen as "mistakes" unless you are able to make them into something good.
For example, it might have been a "mistake" that you became group leader of a bunch of incompetent people, but you can see this as both a learning experience and an opportunity to turn some of your members into less of a lazy bum. If you're majoring in business, you're going to have to get used to leading people, even when you don't get the most ideal group. But it is the leaders who are able to stay persistent and make their company into something who are ultimately recorded in history. Those who rest on their laurels or spend too much time fussing about die out rather quickly.