BOSTON ( TheStreet) -- The benchmark S&P 500 Index earlier this week almost fell into a bear market, defined as a 20% decline from peak to trough. And that's after the index of the largest U.S. companies doubled in two years. What gives?While I myself don't dwell on bull- and bear-market cycles, it sometimes helps to take a step back to see the big picture and tune out the noise. The recently concluded bull market, at least according to some, reached a peak April 29, marking a perfect 100% increase from its start March 7, 2009. The most recent bear market, which is undisputed due to its 56% plunge, began Oct. 12, 2007 and reached a bottom March 6, 2009.