"There's a scurrilous rumour abroad, on self-improvement websites, that Mark Twain is the source of the simpering fridge-magnet quotation. ... Even the genuine Twainisms recycled in countless self-help books—'Age is an issue of mind over matter. If you don't mind, it doesn't matter'—aren't his best. I think I know why. Popular psychology, these days, is a strikingly earnest field; acerbic wit is largely the preserve of cynics who scoff at self-help. It's bizarre: all these grinning gurus preaching happiness, yet without much sense of humour. Twain proved that needn't be so: you can dispense real, uncynical life-wisdom, and still be hilarious."