Mabel

“Junko: That sort of thing happens all the time. You get drunk on your own "correctness," and the more stubborn you get, the further happiness flies away from you. It's a bitter pill to swallow.

Madoka: I wonder if there's any way I can help...

Junko: Even good advice from others won't bring any clear solutions to someone in that frame of mind. ...Even so, you want to find a solution? Then go ahead and screw up. If she's being too correct, then somebody should make mistakes for her.

Madoka: I should screw up...?

Junko: Yep! Tell a really bad lie. Run away in the face of something scary. She may not understand what you're trying to do at first, but there are times when you realize in hindsight that a mistake was the right thing to do... During those times when you're just stuck for an answer, making a mistake is one method of unsticking yourself. Madoka, you've grown up to be a good kid. You don't tell lies, and you don't do bad things. You're a girl who works hard at what she thinks is right. You get an "A" as a child. So before you become an adult, you have to start practicing falling down. You see, we adults have our pride and responsibilities, so it becomes harder and harder to make mistakes.”
― Magica Quartet, Puella Magi Madoka Magica, Vol. 2