The major risks of Zynga stock remain diversifiable risks, and unless you’re willing to trade illegally on inside information about, say, upcoming changes to Facebook’s gaming policies, you should avoid holding a concentrated position in Zynga.
The efficient frontier is still the desirable place to be, and it makes no sense to follow a policy that puts you in a position well below that frontier.
Most of the people who say that “diversification failed” in the financial crisis have in mind not the diversification gains associated with avoiding concentrated investments in companies like Zynga, but the diversification gains that come from investing across many different asset classes, such as domestic stocks, foreign stocks, real estate and bonds. Those critics aren’t challenging the idea of diversification in general – probably because such an effort would be nonsensical.
True, diversification across asset classes didn’t shelter investors from 2008’s turmoil. In that year, the S&P 500 index fell 37%, the MSCI EAFE index (the index of developed markets outside North America) fell by 43%, the MSCI Emerging Market index fell by 53%, the Dow Jones Commodities Index fell by 35%, and the Lehman High Yield Bond Index fell by 26%.