The Vietnamese word "thất ước" is a verb that means "to fail (to keep) one's promise." It is used when someone does not fulfill a commitment or promise they made to another person.
You can use "thất ước" in situations where someone has not done what they said they would do. It can apply to both personal promises and formal commitments.
In more formal contexts, "thất ước" can be used when discussing commitments in professional settings or legal agreements. For example, if a company fails to deliver a service they promised, you could say they have "thất ước" their contractual obligations.
While "thất ước" primarily means to fail in keeping a promise, it can also imply disappointment due to that failure. For instance, if someone feels let down because a promise was not kept, you might say they feel "thất ước."