Something having a limited amount. This is inherent to the nature of business activity, and almost all else. Time is scarce, the universe is not permanent... For some reason, this makes people want to buy stuff. Due to fear of missing out, the permanent loss of something of value (even little value), and the regret of not doing something, would be very high. In fact, the less the thing is (more scarcity), the higher the urgency, which tricks the human brain into making impulsive decisions even without necessity: see artificial scarcity fallacy