Be careful what you promise people. You are not just obliging yourself to keep your promises; other people will hold you to account for them as well. Researchers investigated how the behavior of other people and one’s own behavior influences later behavior. If other people say they trust you, you actually become more trustworthy. If you believe you are trustworthy, you oblige yourself to keep your promises. And other people will hold you to account for them; if you do not keep your promise, you can expect revenge.