Full Idea
When a man fulfils a promise because he thinks he ought to do so, it seems clear that he has no thought of its total consequences; he thinks in fact much more of the past than of the future.
Gist of Idea
Promise-keeping is bound by the past, and is not concerned with consequences
Source
W. David Ross (The Right and the Good [1930], §II)
Book Reference
Ross,W.David: 'The Right and the Good' [OUP 1930], p.17
A Reaction
Not entirely true. It is right and good and useful (etc.) to break a minor promise, in order to achieve major good consequences, like saving someone's life. Promises made when drunk should be reconsidered when sober.