Why There Will Always Be Stock Market Bubbles

This pretty much explains it (from Business Week 12/29/03 issue):

Investors seem to have been reading the headlines about mutual-fund abuses, judging from the increase (to 50%, from 42%) in the share who disagree that small investors can do as well as big investors in the stock market. On the other hand, many remain convinced that they can beat the pros and their fellow dabblers. An overwhelming 75% are confident that the stocks or mutual funds they pick will beat the market averages. That's up from 64% last year. "It's like what Samuel Johnson said about second marriages -- 'the triumph of hope over experience,"' says Laszlo Birinyi Jr., president of Birinyi Associates Inc., a stock market research firm in Westport, Conn.

Also the triumph of hope of the continually updated warnings of, among many others, Burton Malkiel, author of A Random Walk Down Wall Street, Completely Revised and Updated Edition (2003).