The including categories with investment returns that move up and down under different market conditions within a portfolio, an investor can help protect against significant losses. Historically, the returns of the three major asset categories – stocks, bonds, and cash – have not moved up and down at the same time. Market conditions that cause one asset category to do well often cause another asset category to have average or poor returns. By investing in more than one asset category, you'll reduce the risk that you'll lose money and your portfolio's overall investment returns will have a smoother ride. If one asset category's investment return falls, you'll be in a position to counteract your losses in that asset category with better investment returns in another asset category.