Despite having now read far too many self-help books, I still haven't got to the bottom of the Cheesiness Problem. This is the phenomenon whereby some of the most useful psychological insights are also the schmaltziest, such as gratitude diaries, or alternatively the most New Agey, such as the techniques for observing your thoughts explained by Eckhart Tolle in his book The Power Of Now. So let me get this over with quickly, and then maybe it won't be so painful: increasingly, I quite like Oprah Winfrey.

As a rule, mega-celebrities are probably the worst dispensers of life advice, because they almost certainly only got so famous by believing that fame would make them happy - whereas the anecdotal evidence that it doesn't is overwhelming. There are other reasons to distrust Oprah, too. She raved endlessly about The Secret, and frequently promotes its message that having more stuff is the route to fulfilment: she once gave every member of her studio audience a free car. I could do without her sidekick Dr Phil, too, and his "tough love" prescriptions for families whose offspring have committed horrific crimes, such as smoking marijuana.

But something's been happening to Oprah. One sign was that her ratings started to slip, as did circulation of her magazine; her generosity-themed reality show, The Big Give, got cancelled. (All this is good news, in terms of the cheesiness problem - the less popular, the better.) Then she released a series of video interviews called Oprah's Soul Series - far too long for primetime TV's attention span - in which she discussed the subject of happiness with Tolle, along with copper-bottomed scientists such as Jon Kabat-Zinn, a pioneer of mindfulness techniques in hospitals, and the brain researcher Jill Bolte Taylor, although it's true that some more dubious characters pop up, too. But most striking is Oprah herself. She's neither relentlessly upbeat nor overbearingly empathetic, her two basic TV modes; instead, she's questioning, thoughtful, engaged. Pleasingly, her exploration of spirituality enraged some evangelical Christians: one anti-Oprah video on YouTube casts her, in essence, as a cult leader - the evidence being her belief that there are "many paths to what you call God", and that she interviewed someone who wants to replace the Pentagon with a peace department. (Cult leader? Guardian reader, surely.)

Here's my theory. Oprah got so famous that she reached a point most celebrities never do - the point at which she couldn't get any more famous. Sure, the rest of us tell ourselves that fame wouldn't make us happy, but we might just be rationalising our obscurity; Oprah actually got to test the theory that fame, if pursued far enough, would lead to happiness. So perhaps what we're witnessing is almost unprecedented: a mega-celebrity who figures out that celebrity doesn't make her happy and - instead of crashing into drug-fuelled oblivion, or unhinged narcissism - starts wondering, out loud, what might.

oliver.burkeman@theguardian.com