The more expensive stocks get, the higher the chance returns will stagnate or slump. : You’ve more than tripled your money in 10 years by investing in broad U.S. stock market index funds, having weathered a potential double-dip recession (2010), the fiscal cliff (2012-2013), energy-bond volatility (2015) and a transition from presidents Obama to Trump (2016-2017). Nice work! While inaction has been the best course of action since the bull market in U.S. stocks began in early 2009, the risks have now piled up.