Heroic Vow

Most protagonists are depicted as imperfect; though heroic, they aren't flawless paragons of perfection, and will have some minor shortcomings to help the audience identify with them better.

Even so, some characters make a Heroic Vow: a commitment or standard that they will not cross for whatever reason. Perhaps it's a promise to a dear one, a sense of pride, a personal Moral Event Horizon, or just because the hero is a nice guy.

Key to the Heroic Vow is that it is a commitment the character keeps because he willingly wants to. There are no talismans or fail-safes preventing the breaking of the vow, the character's willpower and resolve are the only requirements.

Note that the Heroic Vow doesn't necessarily have to be spoken (or written); a hero's behavior enforced with sheer personal willpower counts. If the vow is spoken/written, it may become a Badass Creed.

Some Heroic Vows are so commonplace, they have their own tropes:
 * Celibate Hero (will not have romantic or sexual relationships)
 * Doesn't Like Guns (will not use firearms)
 * Never Hurt an Innocent
 * Thou Shalt Not Kill (will not commit murder — sometimes won't kill anything)
 * Wouldn't Hurt a Child
 * Wouldn't Hit a Girl
 * Not using a Dangerous Forbidden Technique is requested by a Mentor or self imposed after seeing the potential consequences.