Question: Is breaking a promise to oneself insincerity or lack of will-power?

Sri Chinmoy: When one breaks one's promise, it is undoubtedly due to one's lack of will-power. This lack of will-power is not insincerity. But when the promise is not fulfilled, undoubtedly others may call it an act of insincerity. We say that someone is insincere when he deliberately says something that he knows is wrong and undivine. But lack of will-power is not deliberate. When someone has a lack of will-power, first he consciously or unconsciously has to observe his lack of will-power, and then he has to strengthen his will-power so that he can fulfil his promise. Again, if someone has will-power, that does not mean that he will be able to fulfil his promise. No. The Grace of the Supreme is needed. Otherwise, there are many people who have will-power in abundant measure, but in spite of having will-power, they cannot fulfil their promises. It is because they do not have enough Grace from above. So will-power and Grace from above are both needed to fulfil a divine promise.
Sri Chinmoy, Dipti Nivas, Agni Press, 1976