Nobody knows anything.
William Goldman in Adventures in the Screen Trade
You could counter with “Everybody knows something”, and “Some people know quite a lot, actually”. Think of the doctors who (mostly) help cure our ailments, the engineers whose bridges (mostly) don’t collapse underneath us, the roofers and plumbers who (mostly) allow us leak-free houses to live in.
Then again, think of the over-remunerated investment advisers whose market-prediction performance over a spread of years is beaten by dart-throwing chimpanzees. Think of the providers of corporate IT solutions whose fiendish overhauls end up costing way more and achieving way less than pledged. Think of that class of political and policy experts we innocently rely on to improve society and fend off enemies, whose disastrous errors turn out to have been founded on selective and misleading “evidence”.
Goldman, as a screenwriter, was referring to the Hollywood of immodest studio executives and their surrounding pond-life, none of whom has the formula separating a box-office smash from a flop. But in a funny way his comment sums up the whole smoke-and-mirrors bluster of human civilization.