Mutual funds—and more recently, exchange-traded funds (ETFs)—have offered safety and diversification by allowing individual investors to buy shares in many companies in order to spread risk. It is important for investors to understand what role they play and what role the fund managers’ play in ensuring proper diversification of their portfolio. Additionally, investors need to understand when fund companies fail on proper diversification, how that results in improper diversification and what impact that could have on their portfolios. We highlight what diversification is and why it is important, then discuss why an appearance of being diversified may not mean that your portfolio is truly diversified. Finally, we identify ways that fund managers and investors can damage their portfolio diversification.