You are riding a wave of genuinely positive feelings, and then out of the blue, it hits you: The other shoe is about to drop. It takes root as a nagging worry, and then, sure enough, you accidentally lock yourself in the storeroom, your mysterious allergy flares up, or you pick a fight with your significant other, dog, neighbor, or fill-in-the-blank. When things are a little too good, trouble is … wait for it … not far behind. Or so it seems. What exactly is going on here?