It may be, as one correspondent wrote last week, that advertising works on the "80/80 principle", the assumption that 80 per cent of Australians have an IQ average of 80. Now I'm fine with stupidity in advertising. Indeed, I expect nothing less - isn't that why God gave us the mute button? But what makes the 80/80 thought especially gripping - as in, by the throat - is how much it explains that branch of advertising we call politics.

This is all about scale, or if you like, dosage - a thing whose implications we perpetually refuse to grasp, although they are increasingly hard to ignore.

We're used to the idea of economies of scale, the savings in time or money reaped by producing something - from attack helicopters to graduate dentists - en masse. We're not as good at getting our heads around the costs of scale, how a small personal indulgence blows out, when repeated over time and space, into planetary destruction.

Everything is dose related. Whether it's arsenic in your diet or radioactivity in the sea, small amounts now and then are OK, even beneficial, but large amounts, repeatedly, are bad and even terminal. It's the same with almost everything else - cars, houses, chocolate, holidays, even happiness.

For one person to live in an acre of grass and trees is perfectly harmless, even lovable. But for the numberless hordes to do it means an end to wilderness, clean air and polar bears. This must be obvious to everyone who has ever sat in the daily Sydney-to-Richmond traffic jam, yet we do not see it. Which is why premiers repeatedly stake their careers on building more roads, which just means more congestion. We don't have to be dumb. It's enough that our leaders think we are, and pander accordingly.