Why does a prepaid annual gym fee push visits hardest right after payment, not ten months later?

Answer: The sunk cost fades

Habits strengthen slowly — Not quite. Habits can strengthen with repetition, but the payment effect points the other way. Payment-depreciation research predicts that as a past cost feels more distant, its power to push consumption falls, so the prepaid fee is loudest soon after it is paid.

The fee stays vivid — Not quite. If the fee stayed vivid, it would keep pushing visits later in the year. Payment-depreciation predicts the opposite: the old payment stops feeling like a live reason to show up, even though the unused membership still has value.

The sunk cost fades ✓ — Right. Sunk-cost pressure is strongest when the payment is mentally fresh, then it depreciates. That is why prepaying can motivate early attendance without guaranteeing month-ten attendance: the pain of wasting the fee gets quieter over time.