break a promise 违背诺言；食言；不守诺言；违约

【例句】
Difficulties with children will surface if you try to break a promise you made.
若不履行对孩子的诺言，你与他们的矛盾将浮出水面。

People want to do friends favors and hate to break a promise.
人们总希望朋友间互相帮助，憎恶背信弃义。