So we use others as a helpful shortcut. A filter. If a book is on the best-seller list, we’re more likely to skim the description. If a song is already popular, we’re more likely to give it a listen. Following others saves us time and effort and (hopefully) leads us to something we’re more likely to enjoy.
Does that mean we’ll like all those books or songs ourselves? Not necessarily. But we’re more likely to check them out and give them a try. And given the thousands of competing options out there, this increased attention is enough to give those items a boost.
Knowing others liked something also encourages people to give it the benefit of the doubt. Appearing on the best-seller list provides an air of credibility.