For years, YouTube star Hank Green has stuck to the same straightforward investing wisdom touted by legends like Warren Buffett: Put your money in an S&P 500 index fund and leave it alone. It’s advice that has paid off handsomely for millions of investors: This year alone, the index is up roughly some 16% and averaged more than 20% in gains over the past three years and roughly 14.6% over the past two decades. In most cases, it has easily beaten investors who try to pick individual stocks like Tesla or Me ...