Milkman made people crave the gym by locking their favorite audiobooks inside it

By the early 2010s, decades of research on self-control had converged on two levers for getting people to do a 'should' behavior like exercising: give them a reason to want it more (education, social pressure, reminders) or make skipping it cost something (commitment contracts that forfeit a deposit, fines, public accountability). Both levers fight the same uphill battle, because the should behavior's benefits are real but distant, while the pull away from it — the couch, a show, a snack — is immediate and needs no willpower at all.

Milkman had noticed the asymmetry in her own life: she only let herself listen to page-turner novels like The Hunger Games while at the gym, and found herself wanting to go. But nobody had studied whether deliberately withholding an already-loved indulgence except during a should-behavior actually created new motivation, or whether it was just a personal quirk that happened to work on her — and no version of the standard commitment-device literature, built around penalties for failing to show up, tested rewarding presence with something people already craved.

Locked tempting audiobooks to the gym so wanting the story and wanting to work out became the same want, letting the craving pull people in without external enforcement.

The audiobook's immediate appeal overrides the delayed benefit of exercise, making the gym visit instantly rewarding.

Restricting access to the audiobook only at the gym creates a single gate for both want and should, so the impulse to listen pulls the person to the gym.

The restriction is self-enforcing, requiring no external monitoring or penalties, as the device only works at the gym.

Participants valued the restriction enough to pay for it, showing the intervention created genuine demand for self-control.

Bundle a desired indulgence with a low-motivation task, restricting access to the indulgence only during the task, so existing cravings drive the behavior.

Participants with gym-only audiobook access visited the gym 51% more often than the control group and 29% more than the group merely asked to self-restrict — a gap that persisted, if weakened, through a Thanksgiving-week attendance crash that hit all three groups. After the study ended, 61% of participants chose to pay (an average of $6.91) to keep gym-only restrictions on their own iPods, revealing real demand for a device that took choice away from them on purpose.