In 2003, American management consultant Fred Reichheld invented a system to measure how customers perceive companies, which he called Net Promoter Score (NPS). The premise was straightforward. Asking one simple question could determine customer loyalty: “How likely is it that you would recommend our company to a friend or colleague?” The more a person was willing to promote a business, the better the chances that they’d return themselves. But over two decades, this simple idea has taken on a life of its own.

Whether talking to an airline, dealing with a delivery service or ordering takeout, customers are now often asked for feedback after each communication. The assumption by a customer filling out these forms is that their smiley face, number grade or written response will be use...