Should you ever break a commitment? If so, under what circumstances?

For me this is about balancing personal needs against your word and/or against the responsibilities you have voluntarily taken on. At some point, the damage you do to yourself by keeping the commitment becomes very large. Sometimes too large to bear. Although I think some people still keep to their commitments even if it kills them. Is that reasonable? Why would someone go that far?

Assuming it isn’t reasonable to die for your commitments, is there a general principal we can use to decide when it is time to break the commitment?