The promise remembered by one person can be a passing remark in another’s account.

Two people can leave the same conversation holding very different objects. One heard a commitment and has been building on it since; the other made a friendly noise on the way out of a room and forgot it by the afternoon. Neither is lying when the disagreement surfaces, which is what makes it so difficult to resolve. Weight is assigned by the listener as much as by the speaker.

When something matters, confirm it in writing, briefly and without ceremony. And be careful with casual encouragement, since a sentence that costs you nothing can be carried for months by somebody who needed it to be true.