Keeping your word when it costs you

Made a promise to help a buddy move this weekend but got invited to something really fun with my family. My gut says I go help my buddy anyway because you keep your word. My wife thinks I'm crazy. But if a man's word doesn't mean anything, what does he have? Raised to believe your reputation is everything. Maybe I'm old school but I'd rather be known as someone you can count on than someone fun. Anyone else take this stuff seriously still?