Bias

The availability heuristic, giving undue weight to evidence that is easily available, makes it more likely that people focus on what has happened recently. This can be added to the technical things like 'noise trader risk' to explain some of the short term bubble creation.

Peter McCluskey

People who carefully looked for and evaluated as much relevant evidence as they could saw some chance of the current panic happening, regardless of whether they used intuition or fancy statistical models. Some of them warned of the risk. But it was hard for most people to worry about warnings that had been consistently wrong under all the conditions that were fresh in their minds.

Resisting peer pressure isn't pleasant. The banker who insisted on a 20% down payment for all mortgages got less business during the bubble and was seen by his colleagues as a burden on the bank and an obstacle to helping customers. The regulator who insisted on a 20% down payment for all mortgages was seen as denying the poor the good investments that were available to the rest of the country, and as an obstacle to home ownership (sometimes better described as home borrowing)(governments think home ownership ought to be encouraged, in spite of (or because of?) its tendency to increase unemployment).