A friend who sometimes solicits my advice on investing matters -- for anonymity's sake, we'll call him "Dad" -- often floats trial balloons my way about potential tweaks in his portfolio. After checking his quarterly statement the other day, this friend said he was considering lightening up on the Vanguard TIPS fund I recommended, which happened to be the worst performer among the stock and bond funds he owns this past quarter. "But Dad," I said, "If the stock market retrenches, you are going to love that TIPS fund because it offers a hedge against inflation as well as a great diversification tool against equities. In many down quarters, it will probably end up the best performer in your portfolio." I spared him my usual discourse on how excessive tinkering with one's portfolio based on short-term performance is one of the most damaging things an investor can do, and stuck with the following explanation of how TIPS work and why they serve the dual function of being a safe investment and a great portfolio diversifier.