Keynes Explains The Current Market

Let's do ourselves a favor and stop trying to intellectually understand this market move. There's a reason that markets don't move up and down in straight lines, and it has nothing to do with "fundamentals." The economy is recovering, Greece is saved, austerity is destroying the EU, this is the start of the new bull market, we're headed for inflation, or deflation. None of that shit matters. From Chapter 12 of Lord Keynes' General Theory.

In abnormal times in particular, when the hypothesis of an indefinite continuance of the existing state of affairs is less plausible than usual even though there no express grounds to anticipate a definite change, the market will be subject to waves of optimistic and pessimistic sentiment, which are unreasoning and yet in a sense legitimate where no solid basis exists for a reasonable calculation

Even apart from the instability due to speculation, there is the instability due to the characteristic of human nature that a large proportion of our positive activities depend on spontaneous optimism rather than on a mathematical expectation, whether moral or hedonistic or economic.