NEW YORK (ETF Expert) --The S&P 500 has not merely been resilient in its six consecutive weeks of gains, it has been unstoppable in its 8.3% unrealized run-up.Granted, nearly everyone expects a period of mild selling activity (a.k.a. "a breather"). Indeed, history certainly suggests that unbridled enthusiasm usually gets a reality check or three. The most popular bugbears? Think in terms of the automatic spending cuts to defense, a free-falling yen and Spain's rocky road in 2013. In fact, iShares MSCI Spain ( EWP) is struggling at its 50-day support.