Can We Game Investment Cycles?

So the S&P 500 Index closed the first quarter of 2013 with an impressive gain of 10.61%.. That three-month performance already exceeds the 9.84% annualized return from January 1, 1926-December 31, 2012 (Source: S&P 500 Index Services). Should an investor declare victory for 2013, cash in his chips and sit out the rest of the year with the stock proceeds hiding in the comfort of riskless T-bills? And a related question: can one improve upon investment performance by adopting an investment cycle d...