You promised to help a friend move, but you are exhausted. Would you go?

The context

On Monday you told your friend Luis that you would help him move on Saturday. Luis rented a van. He has to get the furniture out before noon because he is handing over the keys to his old apartment that day.

During the week you worked late on four nights. By Friday you are very tired and need to rest on Saturday. Luis still expects you to come. If you say no, he will have only a few hours to find someone else. If you go, you will keep your promise but will not be able to rest.

You can help all morning, tell him tonight that you will not come, or help for just an hour. Luis organized the move counting on you. You need to recover. You have to decide what to do and tell him today.