You can, but if everyone tried that at once then the price would fall, and most people wouldn't get as much money as they think they now have. So in that sense

You can, but if everyone tried that at once then the price would fall, and most people wouldn't get as much money as they think they now have. So in that sense company valuations are not real. We might pretend that Tesla is worth 2100 USD per share until someone shouts: "Emperor is naked"