"Once stock prices reach the point at which it is hard to value them by logical methodology, stocks will be bought as they were in the late 1920s not for investment but to be unloaded at a still higher price. The ensuing break could be disastrous because panic psychology cannot be summarily altered or reversed by easing money policies."
Alan Greenspan, 1959
The Fed and its acolytes in the banking system sometimes foster an environment where equity prices rise in a steady manner, with little solid underpinning. The higher they go, the further they slide away from rational valuations, the less is required for them to take a tumble.
At the extreme, it can be a bit of a mystery and rather difficult to determine what exactly caused the market collapse. This is how it was with the Great Crash of 1929. Most often it can be something mundane and seen before, but at that stage of the bubble's ascent can cause a fatal break in confidence. And then comes the deluge. And confidence is not so easily restored.
