This column originally appeared on Real Money Pro at 8:51 a.m. EDT on Sept. 23.NEW YORK ( Real Money) -- There is a growing and consensus view that there are no meaningful risks to the U.S. stock market and that the conspicuous P/E multiple expansion (from under 14x to over 16x) seen thus far in 2013 may have room to further expand. This optimistic view permeates the business media and has been embraced by most Wall Street strategists, by retail investors and by many hedge funds and other institutions. We are, it seems, in a bull market in confidence as well a bull market in complacency. Indeed, several weeks ago CNBC's Simon Hobbs asked his guests whether there was any argument whatsoever against a continuing bull market. (Note: I have no idea whether Simon was serious or facetious in his questioning.) To me, the only certainty is the lack of certainty. (My guide is the history of the ups and downs of markets.) Those that hold to certainty of belief (whether it be bullish or bearish) should be hidden in a closet away from children and from money managers that behave like children. Today's opening missive will question the unwavering bullish self-confidence that always seems to appear at or near the end of a maturing bull market as well as the rising belief that there is no downside risk to the U.S. stock market.