Unless you’re a witch (you’re not), your contracts don’t manifest fully formed out of thin air. They're the product of a negotiation, and whether long or short, the process will consist of you and the other party generating ideas about what the deal will look like. Sometimes during the negotiation, one of you may make a promise that for whatever reason doesn’t end up in the final written agreement. But when the other party assumes it’s still part of the deal, that’s when things can get FUBAR.