What did the famous merchant mean by saying half of advertising spend is wasted, and what's the operational lesson? The quote captures both a reality every advertiser faces and the precise problem that direct response marketing was built to solve. The line, attributed to several merchants of yesteryear including John Wanamaker, runs: "Fifty percent of my advertising is a complete waste of my money. Now if I could only figure out which fifty percent, I could save a fortune." The realism is that most advertising spend underperforms expectations. The challenge is that without measurement, the advertiser cannot tell which spend worked [...]