The story you will find almost everywhere is that a circus performer named Dan Rice campaigned for Zachary Taylor from his band's wagon in 1848. Rice's own biographer says that campaign never happened, and the political sense of the phrase does not appear until decades after the word itself is first recorded, in 1849. What is documented is plainer: bandwagon meant the wagon carrying a circus band, and by 1899 on the bandwagon had become a description of joining a winning side.

The economics arrived first: Harvey Leibenstein named the bandwagon effect in a 1950 paper on consumer demand. The nearest psychology is Solomon Asch's line-judgment experiments, published from 1951. Participants were asked which of three lines matched a reference line — a task so easy that people alone got it right over 99% of the time. Placed in a group where everyone else confidently gave the same wrong answer, roughly three-quarters of participants conformed at least once, and about a third of critical trials went to the group's answer.

But the honest version of this includes a defence. Following the crowd is often correct: when other people may have information you lack, their behaviour is genuine evidence, and the queue outside the restaurant frequently does mean the food is good. What separates the useful case from the bandwagon effect is whether the count is tracking anything independent — because sales generate sales, follower counts buy follower counts, and rank quickly starts measuring nothing but its own momentum. The signal and the noise look identical from outside, which is exactly why the tactic has kept working since 1849.