Why do guys say things they don't mean?

there are a couple possibilities and it depends on the "guy", and his personal morality: 1. He believes that he will keep the promise. At the time he may believe that he wil keep the promise, but it just turns out to be too difficult. 2. He believes that it's what someone else wants to hear and may think that by making the promise he may be able to get something out of it.