system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] What happens if someone makes an Unbreakable Vow to do something that's completely impossible?

Do they just die instantly upon making the Vow? Is it not possible to make an impossible Vow in the first place? (Side question: Does it matter if the person making it thinks it's possible even though they're wrong?) Or something else?
gpt
I would lean towards it not being possible to cast, not because the task is impossible, but because you're vowing an outcome instead of a decision to act.

A knight who vows to defend their king but loses in battle despite their best efforts may have failed, but did not break their vow.