The more someone spends with your brand, the more they feel entitled to a higher chance of receiving a random reward. If you have a loyalty program that gives away something for free every month, your most loyal customers, regardless of the fact that all of your customers are in the running to win, believe they have an advantage.
This behavior is called the Irrational Winner Effect. When we spend more time and money with a company, we believe we will get preferential treatment. This belief is further supported through loyalty programs and great customer service. But when we are entered into an uncertain situation in which we have an equal chance of winning something as every other customer, we will think that we have the upper hand.
This tactic can be used to increase the completion of otherwise mundane or boring tasks, such as training programs. By adding uncertain, or even random, rewards for those who have already demonstrated engagement and loyalty, the completion rate of a particular task will likely increase.