​People are bombarded with so much marketing, they need to be reminded of the brand close to the purchase decision so that the brand’s mental associations can work their magic. This is why short-term activation media are widely used in conjunction with media that build predisposition longer term. Brand building media put the ball in the vicinity of the goal and activation media head it home.

Here are some videos/animations designed to explain the concept in more detail:
A video clip from YouTube
A 1-minute animation
A 6-minute audio clip from a podcast