The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.By David Sterman NEW YORK ( StreetAuthority) -- I've been looking at stocks since I was in high school, back in the late 1970s. I eventually chose to turn my fascination with investments into a career. I figured stocks represented the single-best path to wealth creation, thanks to one simple statistic: If you hold an investment for an extended period, then history shows that riskier investments will generate better returns. This means during any 20-year period going back to the Great Depression, stocks always outperformed bonds, and bonds always outperformed cash. Because I was planning on a 50-year career, I was well prepared for short-term plunges, with the expectation that stocks would make up lost ground -- and then some -- during the subsequent decade. That axiom still applies here in the U.S. The S&P 500 has more than doubled in value since 1990, even with the gut-wrenching past few years. But for Japan, that axiom is no longer true. Home to the world's second-largest economy, Japan has seen its main stock index, the Nikkei, tumble, tumble again and tumble some more during the past 20 years. Take a look.