(Read more: Where to find bigger stock market gains: Stephanie Link)
O'Rourke said that the S&P 500, whose all-time intraday high was 1,698, would likely head toward 1,500 in the next six to 12 months.
"There's so many uncertainties out there," he added. "I view my job as measuring risk vs. opportunity, and I see a lot of risk that can unfold in the second half of this year that people seem to be ignoring for the time being."
O'Rourke offered a historical perspective.
(Read more: Defense stocks are overextended: Carter Worth)
"From 1928, 1930, to 2000, the U.S. economy grew 3 to 3½ percent a year," he said. "Since 2000, we've grown 1.7 percent a year. Even if you forget about the Great Recession, you go to 2007, we grew at 2½ percent a year."
O'Rourke said that the so-called "Great Rotation" from bonds into stocks carried inherent risk.
"If you see a 'Great Rotation' occur at this point, the sell-side has trained investors to watch for the 'Great Rotation' and then participate in it," he added.
— By CNBC's Bruno J. Navarro. Follow him on Twitter @Bruno_J_Navarro.
Trader disclosure: On Aug. 9, 2013, the following stocks and commodities mentioned or intended to be mentioned on CNBC's "Fast Money" were owned by the "Fast Money" traders: Simon Baker is long AAPL ; Simon Baker is long GOOG; Simon Baker is long NFLX; Simon Baker is long C; Simon Baker is long RAX; Simon Baker is long PCLN; Simon Baker is long MSFT; Stephen Weiss is short JCP; Stephen Weiss is long BBRY; Stephen Weiss is long POT; Stephen Weiss is long MOS; Pete Najarian is long AAPL; Pete Najarian is long BAC; Pete Najarian is long C; Pete Najarian is long BBRY; Pete Najarian is long SBUX; Pete Najarian is long FB; Pete Najarian is long VALE; Pete Najarian is long NSC; Pete Najarian is long BMY; Pete Najarian is long PFE; Pete Najarian is long MRK; Pete Najarian is long LLY; Pete Najarian is long KRE; Pete Najarian is long EMC; Pete Najarian is long COP; Stephanie Link is long AAPL; Stephanie Link is long JPM; Stephanie Link is long WFC; Stephanie Link is long CSCO; Stephanie Link is long FB; Stephanie Link is long JOY; Stephanie Link is long GPS; Stephanie Link is long VALE; Stephanie Link is long EBAY; Stephanie Link is long YUM.