I saw bank booms ... land booms, silver booms, booms, and they all had one thing in common—they always burst.

The formation of bubbles isn’t so much about people irrationally participating in long-term investing. They’re about people somewhat rationally moving toward short-term trading to capture momentum that had been feeding on itself.

Bubbles aren’t so much about valuations rising. That’s just a symptom of something else: time horizons shrinking as more short-term traders enter the playing field.

Our survey of historical bubbles makes clear that the bursting of bubbles has invariably been followed by severe disruptions in real economic activity. The fallout from asset-price bubbles has not been confined to speculators. Bubbles are particularly dangerous when they are associated with a credit boom and widespread increases in leverage both for consumers and for financial institutions.

We had a bubble in housing.

Forget the housing, bond or derivatives bubbles … Fraud Is the Biggest Bubble of all time

In the mean time, innumerable joint-stock companies started up everywhere. They soon received the name of Bubbles, the most appropriate that imagination could devise.

Double, treble, quadruple bubble, watch the stock market get into trouble...

Over the past 15 years, both Internet stocks and houses have demonstrated the extraordinary excesses that can be created by combining an initially sensible thesis with well-publicized rising prices. In these bubbles, an army of originally skeptical investors succumbed to the “proof” delivered by the market, and the pool of buyers — for a time — expanded sufficiently to keep the bandwagon rolling. But bubbles blown large enough inevitably pop. And then the old proverb is confirmed once again: “What the wise man does in the beginning, the fool does in the end.

Stock market bubbles don't grow out of thin air. They have a solid basis in reality — but reality as distorted by a misconception. Under normal conditions misconceptions are self-correcting, and the markets tend toward some kind of equilibrium. Occasionally, a misconception is reinforced by a trend prevailing in reality, and that is when a boom-bust process gets under way. Eventually the gap between reality and its false interpretation becomes unsustainable, and the bubble bursts.

The most serious problems lie in the financial sphere, where the economy’s debt overhead has grown more rapidly than the ‘real’ economy’s ability to carry this debt. … The essence of the global financial bubble is that savings are diverted to inflate the stock market, bond market and real estate prices rather than to build new factories and employ more labor.

o In bubbles, infatuation with market momentum takes over from any notion of value and fair price, and greed (plus the pain of standing by as others make seemingly easy money) neutralises any prudence that might otherwise hold sway.

Having written all that, I must admit that there is some soul searching going on in the economics profession. As obvious as the financial crisis seems after the fact, few economists saw it coming (with some notable exceptions). Virtually none anticipated how severe it might be. In the fall of 2005, several prominent economists wrote in a prestigious journal, “As of the end of 2004, our analysis reveals little evidence of a housing bubble.”
Wrong. Actually the article was worse than wrong, because it was written explicitly to refute the signs of a bubble that had become obvious to many laypeople—which is kind of like the fire department showing up at a house with smoke wafting from the roof and declaring, “No, that’s not a fire,” only to have flames start leaping from the attic twenty minutes later. There was a bubble. And it can be explained best by incorporating psychology into economics, namely the tendency of individuals to believe that whatever is happening now is what’s most likely to happen in the future.

In bubbles, infatuation with market momentum takes over from any notion of value and fair price, and greed (plus the pain of standing by as others make seemingly easy money) neutralises any prudence that might otherwise hold sway.