Why a 10% chance of a free product drives more action than a guaranteed 5% coupon. Human beings are wired for uncertainty. It’s the reason we check our phones even when they haven't buzzed. It's why we watch sports live instead of reading the score later. And it is the reason why "mystery boxes" on YouTube get millions of views while unboxing a standard package gets none. In the world of loyalty, however, most brands ignore this psychology completely. They offer Fixed Rewar