Equestria has a lot of rules for a lot of different things, different occasions, and dealing with different creatures. For instance, you never crack offensive jokes about Luna's stars or moon, you never touch Celestia's cake, you never mess with Twilight's books, and the most serious rule, the rule over all rules...

Never, ever, ever, EVER, in an eternity of millennia, do you ever break a Pinkie Promise.