Also belief and confidence, which is not to be underestimated, because the opposite can bring the whole thing down.
Yes, it's pretty much like a hot air balloon. It needs constant injections of gas to stay aloft. One tear in the fabric and it all plummets earthwards. This is why companies now have to report quarterly, to ensure constant applications of the gas burner. It doesn't do the companies any good (encourages short termism) but it's good for price fluctuation and the speculators make a lot of money out of that, both on the up and the down.
