[thaumasiotes]

On the other hand, I have a Grimm's Fairy Tales including a story that tells how the hero visits a petty king's court and receives a promise conditional on accomplishing something impossible. Off he goes and does the thing, and the narrator makes an aside saying "Now the king would gladly have blown off the promise, but he was trapped because other people in the court had heard him make it."

[anonymouskimmer]

Regicide, and even just murder in general, is highly frowned upon these days. Back then it was de rigueur when the concept of fealty required reciprocity in the keeping of one's word.

[thaumasiotes]

I don't see the connection between your comment and mine?

[anonymouskimmer]

As other people in his court, with whom reciprocal vows of fealty have been made, heard his promise, he now has to keep his promise our of fear of them proactively removing him (or otherwise punishing him, such as by breaking their own vows of fealty) for breaking his promise.

Today one can lie with much more impunity, at best tying things up in court for years until the person you lied to gives up, at worst being ordered by the court to make good on the promise and pay some legal costs (maybe).

As your synopsis shows, it's not prestige that forced integrity, it's the fact that others heard, and presumably would enforce such vows, even against a king, that forced integrity, even from a king.

[thaumasiotes]

I don't think a direct threat of enforcement is the problem. A king who was known to have gone back on his word would be an illegitimate ruler and he would be unable to function as king within his court and his kingdom. He would end up getting deposed, but that wouldn't be part of an effort to enforce the king's promise, it would just be what happens to kings who aren't fit to rule.

The direct consequence of the king breaking his vow is "only" that the king loses his prestige. But the indirect consequences are severe; "king" is a position from which it is not safe to be removed.

[anonymouskimmer]

Yes.