It is famous that Shia jurisprudents has given the green light to break the promise. According to them keeping the promise is at most favorable (Mostahabb) and not obligatory until it has no relation to any contract. But if we analyze their view we see that there was no textual (Lafzi) reason on that time and the concept of all reasons for real rule (Ejtehadi) is the obligation of keeping promise.  Referring to “understandings of believers” and “conduct of faithful men” is the frequent reason which it is evident in jurisprudents’ words. But such a reason encounter two controversies: firstly holding its connection to infallible Imam is not possible, secondly maybe this kind of conduct is because of unawareness and ignorance of believers. Ethically analyzing the issue confirms that breaking the promise is among the negative personality qualities and who commits that would be reproached; So this jurisprudential rule should be reviewed when we make the ethics as the aim of the Islamic rules.