From Richard Smitten's excellent Jesse Livermore biography:
...human nature never changes. Therefore, the stock market never changes. Only the faces, the pockets, the suckers and the manipulators, the wars, the disasters, and the technologies change. The market itself never changes. How can it? Human nature never changes, and human nature runs the market-not reason, not economics, and certainly not logic. It is our human emotions that drive the market, as they do most other things on this planet.