Just because Cambridge Analytica tells its customers it can sway elections, it doesn't follow that they're any good at it

Unilever founder John Wanamaker famously said, "I know that half the money I spend on advertising is wasted. My only problem is that I don't know which half." It's an odd testament to the power of advertising, an industry whose executives are incredibly effective at selling their services to other executives, even if they can't prove they're any good at selling their customers' products to the public. (more")