[ignitionmonkey]

They don't require interaction. Think about billboards, TV/video ads, sponsorship ads, etc. It's enough for you to just see an ad, to not forget a brand or product exists.

At some point, you might think about a product subconsciously due to any reason, and since you saw the ads, you'll think of a specific company's product and likely rank them higher among "unknown" brands by default. That will bubble up at some point and you'll have a desire for it which you either accept or reject. Most will accept, causing more to accept to be in the group. It's human nature.

Any interaction is a bonus.