"For instance, an investor who put $100 into the U.S. stock market in 1927 and dodged out of the market whenever CAPE was 50 per cent or more above its historical median at the time would have wound up with nearly $138,000 in 2016. They would be far behind a simple buy-and-hold investor, who would have seen their $100 grow to more than $320,000."
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That's one child prodigy! Given that we only live +/- 80 years, the fatuous absurdity of these sorts of hypothetical scenarios fully emerges when we take it a pinch more literally: 

"An infant child investor on Jan 1, 1927 who invested $100 into the US stock market [that's $1,395 in 2017 dollars]...and dodged out of the market whenever...would wind up with nearly $138,000 in his/her early-90s."