Every football fan remembers the over-the-top onslaught of commercials from DraftKings and FanDuel during the 2015 NFL season. With every break in the game, someone would pop up on the screen telling fans they could easily make money every week betting on fantasy sports. People quickly got sick of the ads.
But the two companies were tapping into a key marketing concept known as the familiarity principle. Psychologically, the more times people see something, the more they like it. That....