People will remember you by what you do, not by what you said. So if you have made someone a promise, do your very best to deliver on it, and if possible, go the extra mile. Throw in something extra. We all like that. We like to be treated well. So whenever you can, do the same for others. Spreading positive energy around only creates more of it. If for some reason you think that you might not be able to deliver on a promise, it would be best to manage the other person’s expectations by informing him sooner rather than later. Ideally, before you even made the promise but if that is done, than the soonest you realised it.