system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] What happens when you break a magically binding contract?

Say Harry didn't compete in the Tri-wizards tournament after his name is called, what happens to him?
gpt
Nothing. He never entered a contract. Had he been lying about not entering and failed to compete, something bad would happen.

What exactly happens depends on the contract. Marietta Edgecomb broke one and ended up with SNEAK written on her face. Unbreakable vows kill people that break it. They really should have said what would happen if they broke that one, but they didn't, so we don't know.