Manufacture scarcity and let desire do the work.
Two mechanisms, and Worchel's cookie-jar experiment in chapter 5 separates them.
Rarity as a quality signal: scarce things are often scarce because they are good, so scarcity is a usable proxy when you have nothing better. The proxy fires whether or not the rarity has any connection to quality.
And reactance, in Brehm's sense: a threatened freedom produces a motivational surge to reassert it, and the object of the threatened freedom becomes more attractive in the process.
Worchel's crucial results are the operational ones. Newly imposed scarcity beat constant scarcity — the ten-cookie jar swapped for the two-cookie jar produced higher ratings than the jar that had always held two. And scarcity attributed to demand from other people beat scarcity attributed to a supply error.
So the specification is: not scarce, but becoming scarce, because of others.
That is why the effective forms are all dynamic. The countdown rather than the deadline. The stock counter falling. The limited drop with a published end date. The seat map showing eleven other people looking at this flight. The waiting list.
Ty Warner's Beanie Babies are the purest commercial execution. Warner retired individual designs on announced dates, repeatedly, over years, producing a permanent state of anticipated loss around a five-dollar toy and a speculative market with price guides and dedicated magazines. In December 1999 he announced the retirement of the entire line, then reversed it after a public vote. The market collapsed shortly afterwards.
The boundary is factual. Scarcity that exists is information and stating it is honest — the venue holds four hundred, the print run was two thousand. Scarcity that is asserted and does not exist is fraud, and in several jurisdictions specifically actionable: false countdown timers, fabricated stock levels and invented competing bidders have all been the subject of enforcement action.
The tell that separates the two, and it is the counter as well, is that real constraints have causes a person can state, and manufactured ones are asserted without explanation. If the answer to why does this expire at midnight is a fact about the offer rather than a fact about the world, there is nothing behind it.
The counter is chapter 303.
Countered by The Countdown That Never Ends