After acquiring several small grocery stores in 1934, Sylvan Goldman noticed that his customers would stop buying items when their hand-held shopping baskets became too heavy. This led him to develop the shopping cart. In its earliest form, the invention was a folding chair equipped with wheels and a pair of heavy metal baskets. However, despite keeping them in prominent places and with huge signs, his customers didn’t use it – men thought it ‘effeminate,’ and women felt it demeaned their ability to carry a shopping basket.
Frustrated to the point of giving up, Goldman tried one more tactic – he hired shoppers to wheel the carts through the store while accumulating the items they wanted to purchase. Encouraged by some initial success, he continued paying people to push his shopping cart for two straight years(!).
Over time, his customers adopted.. and the rest, as they say, is history. Even if his shopping cart was a superior product, it required Goldman to use the principle of social proof to transform it into a success story.
Nothing draws a crowd… like a crowd. – PT Barnum
Source and thanks to: Griskevicius, Cialdini, and Goldstein – Applying and Resisting Peer influence