If you think about it, 2013 was The Teflon Year for stocks: ALL the disaster predictions failed to materialize.
Think of all the reasons you had to sell in 2013: the fiscal cliff, sequester, taper, Syria, government shutdown, debt ceiling...and we are at highs. The only issue that caused stocks to pause mid-year was the potential for higher rates. Of course, central banks...from Japan to Europe to the U.S....were actively involved this year, and there is no doubt they helped stabilize global markets. The 'Central Bank Put' was very much in evidence.
Now, bulls argue, with a budget deal and the taper starting, we have greatly reduced macro risk for the next 2 to 3 months. True, we won't know the full effect of the taper for many months, but right now look at the action: the S&P 500 is up almost four percent in the last two weeks, and the small-cap Russell 2000, considered a good gauge of stock market risk, has outperformed almost every day since the taper was announced.