Brands love reaching their most passionate customers. As a former retail CMO myself, I get it. When you reach early planners, you reach the CEOs of the household—an audience that buys and spends more. Reach them first, and you have a shot at being their first choice when it’s time to shop.

And yet, for as long as marketers and advertisers have been prioritising planners, they’re making some seriously incorrect assumptions about this key audience right now. I heard from a CMO...