Nothing happens until somebody sells something. Not war, not peace, not the adoption of fire or the wheel. Not penicillin or PCs or deodorants that are strong enough for a man but made for a woman. Every idea, no matter how self-evidently brilliant or idiotic, has to be sold. And that, in 50 words or less, is why there's so much advertising out there.

Every space has become ad space. Everything from sports arenas to nature walks and kazoo players are sponsored, branded, and bartered. You're soaking in it. Blasted, assaulted, insulted, surrounded, distracted, hypnotized, and occasionally seduced by countless commercial messages each day. Ads flying in the sky, painted on the streets, projected onto buildings, driving by on taxi-tops, chattering on electronic devices. No amount of plastic sheeting and duct tape can shut them out.

Ad clutter has increased every year for two decades, but lately it's become overwhelming. In 2002, every hour of daytime network TV contained nearly 21 minutes of commercials. Some cable networks have 60 seconds of ads for every 140 seconds of programming. The average fall fashion magazine requires a reader to flip through 128 pages before getting to an actual article. Thirty percent of email is 100 percent pure spam.

Something interesting happens in the midst of all this noise: The value of any given ad erodes. A viewer's ability to recall a given message drops 45 percent when the number of ads in a commercial break doubles, according to Nielsen Media Research. Advertising has the most impact in countries with low clutter – Belgium, Denmark, the Netherlands – and the least impact in the most saturated countries: Japan, Hong Kong, Italy, and Spain.

What's it all mean? The 300-year-old advertising ecosystem – where marketers subsidize media in exchange for the chance to make an impression on consumers – may finally be breaking down. Advertising built its power on the ability to interrupt your busy day and put a new idea in your head. A snippet of a promise, an image, a design that may make a product seem more familiar when you see it in a store, even if the commercial itself irritated the hell out of you. Now, too many messages, too many channels, too much junk, have led to a global case of ADD.

Overloaded consumers flee advertising by leaving the room, turning the page, or just glazing over. And digital tools – from pop-up blockers to PVRs – are taking over where the remote control leaves off. Hollywood and Madison Avenue are fighting back with neat tricks like the undeletable gigabyte. But the fact remains that advertising is running out of space in the most important medium of all – the human brain. It takes a great mind to hold two opposing thoughts. It takes a third-stage schizophrenic to hold 52 makes of automobiles and 55 brands of cereal.

The solution is the same as it's always been: Do better ads – the kind people talk about around the water cooler, or point out in magazines. Occasionally, ads can be so good that they become part of culture, works of art or protest or comedy that resonate far beyond their initial intent. Which is, always and unfailingly, to sell something.