When quality perception has a hiccup, that’s a tasty opportunity for the competition. There’s a mini-revolt afoot in the candy aisle. Fans of Reese’s Peanut Butter Cups, including a grandson of the original inventor, have publicly criticized newer iterations of the dominant brand, pointing to a drier, chalkier filling. Whether that critique is universal (or even accurate) is beside the point. What matters is that enough consumers believe it. For whatever reason, there’s been no shortage of...