For decades, Bed Bath & Beyond mailed out a 20% off coupon so omnipresent it became a cultural artifact — tucked in junk drawers, hoarded by grandmothers, honored years past expiration. But that little blue-and-white rectangle wasn't a marketing masterstroke; it was a slow-acting poison that collapsed margins, addicted customers to discounts, and made the company structurally incapable of surviving the moment retail actually changed.