100 percent stocks can be a risky investment strategy - unless you're young and can handle the ups and down of the market for a decade or two. Does that sound like insanity? Or even irritational exuberance? It certainly hits at both. But based on the numbers, investing 100 percent in stocks until your 40 really can be the best investment strategy for young people. The long-term trend is clear that stocks rise over the decades, even if they have a few bad years along the way. If you're under 40, you have enough time to capitalize on the long-term uptrend, as well as to ride out the inevitable declines along the way. Capitalizing on the long-term trend Between 1928 and 2016 the S&P 500 had an average return of right around 10 percent. Few asset classes of any kind have come that close for so long. Meanwhile, the 88-year time frame covers a healthy human life span. In even given decade, stocks can and do crash. If you have no more than a decade to plan for, you certainly...