Hobgoblin Witchmaster: "Boss! Boss! I just found this awesome trap that's guaranteed to whoop the hell out of anyone who opens whatever chest we rig it up with...."
Hobgoblin Chieftain: "That's great. Plant it inside the very last chest. The one where we keep all the good stuff."
Hobgoblin Witchmaster: "But Boss, shouldn't we reverse engineer this trap so we can figure out how to replicate it and apply it to every treasure chest in the place?"
Hobgoblin Chieftain: "Not at all. If you do that, they'll be expecting it when they go to open the last chest, and they'll be a lot more cautious. They might not even open that last chest at all. So every other chest before the big chest will have the usual five-and-dime traps. Then, when the heroes get to the last chest, they'll be thinking 'Oh, every other chest in here had a cheap trap on it because these podunk hobgoblins can't rig up a decent trap to save their mothers' souls, and this trap's no different.' Then, POW! They'll stick their faces right in it, and our trap will blast those faces right off."
Hobgoblin Witchmaster: "Whoa. That's pretty sadistic. Good thinking, Boss!"
Hobgoblin Chieftain: "I know."