Like a fine wine that only gradually surrenders its nuances to the drinker, The Secret - still the bestselling book on Amazon in both the new age and psychology categories - reveals new depths of forehead-smacking idiocy each time I return to it. The latest comes in a trailer for the DVD version, which includes several affirmations that will allegedly bring unimaginable riches. One is, "Everything I touch turns to gold." A man is shown touching a statue, which turns golden; he looks elated. I don't mean to quibble, but would it be fair to say that's not quite the point of the original King Midas myth? Didn't he discover some downsides? Another is, "Money falls like an avalanche over me." Think about that. It wouldn't be pleasant at all, would it? In fact, it'd probably kill you.

The Secret is in a class of its own, nonsense-wise, but obtaining wealth lies at the heart of many self-help prescriptions. The standard, rather pious counterargument is that money can't buy true happiness. But there's another objection: sometimes, you can buy happiness with less money than you think.

This view is clarified in Vagabonding, a recently re-released book on long-term travel by Rolf Potts, who recalls his astonishment when he heard Charlie Sheen's character, in the film Wall Street, defending his punishing work schedule: "If I can make a bundle of cash before I'm 30 and get out of this racket, I'll be able to ride my motorcycle across China." Potts writes: "[You] could work for eight months as a toilet cleaner and have enough money to ride a motorcycle across China." Tim Ferriss, author of the hyperbolic but interesting bestseller The 4-Hour Workweek, recalls a friend saying that if he stuck out his job in finance for eight years, he'd be earning $3m. And what would he do with the cash? "I would take a long trip to Thailand," he replied.

Travel isn't the issue here: that may or may not be what you'd choose to do if you could. The point is our tendency to inflate the resources we think we'd need to pursue our dreams. That's the danger in self-help's focus on "dreaming big": defining an ambition as "big" implies that it's beyond reach. This keeps it safely in the realm of fantasy: if you can convince yourself you can't afford to do something, you're spared having to take the anxiety-provoking actions that might turn it into reality.

And if you do pursue riches, things might not go as planned. When Po Bronson wrote What Should I Do With My Life?, an extraordinary book about people who made major life-changes in pursuit of their "calling", he assumed he'd find many who'd decided to work in a big-money, low-enjoyment job so they could leave with the cash to do what they really wanted. But, in reality, they were still in their jobs long after they'd planned to leave. "You end up so emotionally invested in that world, and psychologically adapted," he writes. "Ten times a day they'd fantasise about [leaving]. But they couldn't."

oliver.burkeman@theguardian.com