Valuation is not an issue while earnings are growing, (10.8% 2013, 7.9% 2014), but the problem is earnings are not growing anymore. At 16.7x forward eps the market is vulnerable to any number of negative effects. Earnings growth, or the lack thereof, is one potential catalyst for a selloff. With an above average valuation, the market has little room to absorb a falloff in earnings growth. So I see one of 3 things happening. First, analysts could raise their earnings estimates. We know the estimates are probably going down and not up, so this seems unlikely. Second, the market could selloff to a more reasonable valuation more in-line with stagnant earnings growth. Third, the market could stay up at this valuation despite earnings growth of 2%. This last one sounds more like wishful thinking than a likely scenario.