The “streetlight effect”: Often told as a joke, of a drunk searching for his keys under a streetlamp instead of the dark alley across the street where he lost them because the light is better there, the same principle applies when managers over-rely on data that’s readily available. Instead of carefully considering which data sources and analytics are likely to drive the firm’s growth strategy, marketers too often set their sights on data that is easy to access, measure, and apply, or on analytics their competitors explore.