Philosophers have been arguing about what it really means to know something for millennia so I don't think we can make any significant progress there. But what

Philosophers have been arguing about what it really means to know something for millennia so I don't think we can make any significant progress there. But what about practical purposes? How do you decide if a mechanic knows enough to fix your car, a dietitian to help you lose weight? A possible life partner how to build a healthy relationship, a friend to give the right life advice? My current rule of thumb is very similar to "knowing how something works = knowing how to work it", meaning one really only knows something if he's already done it in the past. Preferably multiple times. This rule tells you that nobody knows some things, for example things that did not exist in the past so nobody could have done them. How will AI impact our world? What will happen if we rewrite Linux in Rust? What will be the outcome of a new social or economic policy?