8. In Rumpelstilskin we deal with two kinds of promises. First is a miller's claim about his daughter's abilities. He said she can spin gold from straw. King demands a proof and daughter is practically condemned to death.
Unexpectedly a little man offers his help if she makes a promise on her own. She promises him her unborn son (and she is not even pregnant, so this promise doesn't sound too serious if we think she'll be dead without gold in couple of hours anyway).
But little man (Rumpelstiltskin is his name) keeps his promise, she marries a king and after a year they got a son. Rumpelstiltskin demands a boy and his mother is in serious trouble. Fortunately she manages to make another deal. If she guess little man's name, she can keep the boy. Finally she wins, so she doesn't have to keep her promise.
9. We have similar situation with two promises in the Beauty and the Beast. First is father's promise to send his daughter into Beast's castle in exchange for his life. When she (Beauty) comes and step after step falls in love with the Beast, has to promise to return to the castle after visit to her family.
In her home she becomes a victim of intrigues of her sisters and almost forgets to keep her promise. But love conquers all and Beauty returns soon enough to save his life, break a spell and they live happily ever after.
10. Less happy is the ending of the Bluebeard. When he leaves the castle, he gives his keys to his wife and she has to promise not to open one specific door. She break her promise and he wants to punish her with beheading.
She shows regret but Bluebeard stays merciless. This seems too cruel punishment for her act of curiosity anyway and we as readers are totally satisfied with the ending. Bluebeard, serial killer and unforgiving monster dies and his wife, despite breaking her promise, becomes rich heiress.
Apparently under certain circumstances we can break a promise.
And forgiving can be even more important than keeping one's promise!