One of the difficult parts of being a teenager and young adult is that you learn the rhythm and gist of how things operate without actually learning how they operate. This is one of the reasons "being cool" is such a big deal at that age -- the idea is to learn to mimic and fit in with the rest of how society works, not actually to be able to manipulate it. Faking it is much more important than actually doing it. That's what everybody else is doing anyway.
Somewhere in your 30s or 40s (perhaps sooner or later) you realize that much of life is like that: you don't really understand how a car works, only that most of the time you can get in it and go places. When it doesn't work, you take it to another person. She may also not understand what's wrong. But most all of the time she does. If she doesn't, she takes it to another person, and so on. You keep getting closer and closer to total understanding but you never reach 100%. That same pattern applies to medicine, advanced physics, and most everything else. When there's a billion areas of knowledge, even 99% knowledge leaves a helluva lot of holes. There's this surface layer of generalities and half-truths that work so often that it's just not worth diving down into the details on everything else.
On top of that, other people are very happy to share their own generalizations and heuristics, so we're kind of operating in a rumor-of-a-rumor mode. The vast majority of the time it doesn't matter, but sometimes, like when you ask questions about how startups work and most of your surrounding culture gives you bad answers, it does. Most of life isn't a geometric proof built on the linear progress of science; it's a bunch of heuristics strewn together to make something practical that you can use.
What we "know" is a product of generalizations and communications about half-truths from the environment we're in. This is one reason why it's so critical to spend a lot of time challenging the things you think you know, especially in areas that make a big difference to you personally. It also means that you must accept a deep and abiding peacefulness in not knowing very much at all about most of the stuff you actually work with in your day-to-day life.