A promise is limited. A promise is binding only one way. A promise is not forever.
A promise only lives as long as the promiser.
You cannot transfer a promise from one person to another.
Promises need to be renewed and recreated.
Promises are intimate between two people.
Promises are never covenants because covenants are always public and legalistic.
There is no outside binding power in a promise — the inherent morality of those who promise is the only hope the promise will actually be fulfilled.
Promises are static and non-elastic.
Promises are brittle and they live and die in the now — so enjoy them while you can and the exchange of promises is always the best guarantee of reciprocal happiness.