Don’t put all your eggs in one basket. I have no idea where that idiom originated from but it is perhaps the best and simplest way to describe diversification. Instinctively investors know they should diversify their portfolio and most do this. Having looked at hundreds, if not thousands, of portfolios, I can tell you that diversification amounts to more than just owning multiple funds. A common mistake that investors make when trying to diversify their IRA or 401k is that they, inadvertently, create a portfolio that has the illusion of diversification. Let me explain.