“That’s your costume for the Halloween party? You’re dressing as Harry Potter, too?”

“Yep, I resisted for a long time, but I’ve jumped on the bandwagon and become a Harry Potter fan.”

A bandwagon was originally a wagon carrying a band in a parade or circus. Bandwagons began to be used by politicians in the U.S. Now we use the phrase “jump on the bandwagon” to say someone has adopted a popular opinion. If an idea or opinion is very popular with others, it sometimes makes people agree even if they otherwise wouldn’t.