The bandwagon effect is a mental heuristic with an unusually self-explanatory name: it refers to the common human tendency to go along with the judgment of the people around us.
The general rule is that conduct or beliefs spread among people, as fads and trends clearly do, with the probability of any individual adopting it increasing with the proportion who have already done so. As more people come to believe in something, others also "hop on the bandwagon" regardless of the underlying evidence.An excellent example of the bandwagon effect is the iPhone app store, where the vast majority of the money is earned by a very small fraction of available apps. We like the songs that other people like, we go to the restaurants that are already popular, and we buy products that we've seen other people using.
Heuristics exist for a reason: they're convenient rules of thumb that allow us to make quick decisions when it will take too much time or effort to reach a more well-considered decision. The modern world presents us with a bewildering array of choices, and in most circumstances there's not enough information ready at hand to decide which of our choices are best. When you go to the store and are confronted with 15 varieties of peanut butter, you're probably not going to set time aside to research your options. You'll buy a brand that you recognize because the fact that it's already popular insulates you against the possibility that it's a really terrible brand of peanut butter. It might not be excellent, but it will probably be OK, and sometimes that's all we need.
The implications of the bandwagon effect on digital strategy are profound. First, be aware that, in the presence of multiple options, your customers or readers will look for social indicators about which choice to make. If you have a "most popular" list on your site, that will strongly affect user behavior.
When you're selling a product online, the bandwagon effect shows up in user ratings. Whether or not you list ratings of the product you sell, you can expect customers to find ratings somewhere and rely on them in making the choice of which product to buy. If there are no ratings, your customer will feel vulnerable in making the choice to purchase your product and you must make some effort to reassure them.
In short, there's safety in numbers, and danger in their lack. Create confidence by letting your customers know that there's a large and happy community around the product that you're selling.