People value things more when they're in limited supply.
<aside> ℹ️ While scarcity is typically invoked to encourage purchasing behaviors, it can also be used to increase quality by encouraging people to be more judicious with the actions they take. It can come in different forms: Time-limited, Quantity limited, Access-limited. Never fake scarcity if you don't want Reactance
</aside>
You know how it works.
Scarcity is the psychological bias that makes us place a higher value on things that are scarce than those in abundance. Basically, we tend to like things that are harder to obtain.
Feeling that there is only one chance can convince people to take action sooner, sometimes without careful consideration of consequences or alternative options.
The scarcity principle is a well-documented social-psychology phenomenon that causes people to assign high value to things they perceive as being less available. In real life, Black Friday is a good example of scarcity: a sale that occurs on only one day of the year (the day after Thanksgiving in the United States) and consists of a limited number of products offered at discounted prices. In the case of Black Friday, the mobs of eager customers are most often a good thing for retailers…until the mob turns violent.
Scarcity Principle: Making Users Click RIGHT NOW or Lose Out
Scarcity in UX: The psychological bias that became the norm