you don't see the ad and think "wow, that athlete is holding this one brand of cheese, I'm gonna buy it"
you mentally associate those two, and when you go to the supermarket, you see the brand and buy it out of instinct, since that brand gives you a good feeling subconsciously.
or if you ask yourself "I never bought parmesam cheese before, which brand is good? oh I've seen this one before, it must be good"
I mean marketing these days is mostly just shouting brand names at you so that when you arrive at the aisle of 44 differently labeled permutations of the same 3 products made by the same 3 companies you'll make a decision based on "I've heard of this brand before."