Years ago, my colleagues and I conducted a fairly large-scale research project. We interviewed a bunch of high-income professionals who provided professional services. This group included doctors, dentists and lawyers, and like most of us, they earned money only when they were working. In essence, they traded their time for dollars.

Our finding was this: Homes and retirements accounts aside, the most valuable asset they owned was the person staring back at them in the mirror each morning. Chances are, the most valuable investment you own is the investment called you.

A more technical way to think about it is that the most valuable asset you own is the present value of your future earnings. But here’s the problem: Despite what your spouse may tell you, the investment called you is getting less valuable with every year that passes.