Says who? What's the proof?

Last time I asked someone that (over a decade ago), the answer I got was that ad companies wouldn't spend millions of dollars on their ad campaigns if they didn't have proof of effectiveness. Sure, okay, that's good evidence that the ad campaigns are effective at getting some people to buy the product. But what's the evidence that I, personally, am influenced by ads? Rather than "many people are influenced by ads, don't think you're immune"?

Especially because I, personally, actively avoid advertising. I block it on the Internet, I avoid watching live TV and instead buy (or check out from the library) DVDs of shows I'm interested in... And the billboards on the highway are mostly for services I don't need (like injury lawyers) so I have almost never bought something because I saw it advertised on a billboard. The only exceptions are the ones where the billboard said "(name of restaurant) 10 miles ahead" and I thought "Oh good, I had been hoping to find exactly that restaurant, I'll pull over in 10 miles". But I was already looking for that product, the billboard ad just helped me find it.

Not to mention that if all ads were like that — "Hey, our restaurant is at exit 183, we do really good fajitas" — I would be far, FAR less annoyed by advertising. If that was the only kind of ads you saw on the Internet, I might not have sought out adblockers in the first place.