⚠ The Sunk-Cost Wears OffLow threat

The prepaid habit is powerful but not unconditional. It rests on a member believing, roughly, that they get their money's worth — and the day that belief cracks, the same psychology that bound them works in reverse. A member who notices they have used Prime only a handful of times, or who watches the fee climb while their own shopping stays flat, begins to perform the opposite calculation: not 'I must use this' but 'I am paying for something I barely touch.'

The danger sharpens as the fee rises and as free fast shipping becomes ordinary elsewhere. When rivals offer next-day delivery with no membership at all¹, the marginal value of Prime's core benefit thins, and the sunk-cost logic that once favored Amazon has less to hold onto. A benefit that everyone offers for free is a benefit no one will pay a premium to keep.

The counterweight is that Amazon keeps stuffing the bundle with video, music, grocery, and discounts precisely so that no single benefit going commonplace can unravel the whole. The member who shops less may still watch the shows, and the accumulated conveniences keep the renewal reflex alive even when the shipping math weakens.

Call it low-to-moderate and slow-moving. The prepaid habit does not collapse in a season; it erodes at the margin, one lightly using member at a time, and Amazon can defend it by widening the bundle faster than any single perk becomes ordinary — but it cannot raise the price forever without eventually testing the very arithmetic on which the whole habit depends.