The Problem of Cumulative Advantage

"Cumulative advantage" is when small initial successes compound over time to create bigger later advantages. But, whether a particular ad gets a success early, or late, is partially random. So cumulative advantage can increase the randomness of an ad's success.

For example, let's say one ad sees an early success. The ad system could then estimate that it is a better ad, and show it in more competitive placements or lower the cost of each impression so it gets shown more often. This gives that ad more opportunities for further success, so it could outperform ads of the same quality.