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 James Brumley NEW YORK ( StreetAuthority) -- Almost everyone knows Harvard University is one of the premier names in the world of college academia. What most of the world may not realize, however, is that the geniuses managing its $27.6 billion endowment have become the envy of other Wall Street fund managers, and for the right reason -- namely, achieving big and reliable returns with a long-term holding strategy. In the past two decades, the Harvard endowment has averaged annual returns in the 15% to 20% range, a la Warren Buffett. Those numbers easily top the domestic large-cap market (the S&P 500), which has been neither reliable nor all that productive during that time. In fact, the market's average return for the last 10 years is teetering on being negative. So what separates Harvard's gurus from the rest of us? It's probably not what you think.