The reason why this is significant is that the value of human capital is one's largest asset. So it's crucial to effectively manage the risk that it may rise and fall over time. For some people, the value of their human capital can be quite volatile, especially those in corporate and/or entrepreneurial positions, where their personal income can bounce around just like the stock of the company they work for.
By contrast, jobs in more stable industries and professions—such as being a tenured professor or working for the government—produce a consistent employment income, not unlike the ongoing payments from a bond.
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Ultimately, given both the size of the human capital asset and the fact that some careers are more bondlike while others are more stocklike, effective diversification of your entire household balance sheet might even require you to use your financial capital just to counterbalance the risks of human capital.
For instance, those with stocklike careers might own more bonds, while those with bondlike careers can afford to own more stocks. Similarly, decisions about savings should recognize that sometimes, investing in human capital can actually produce a greater return on investment than saving—even better than buying stocks in a Roth individual retirement account for the long run.
So the next time you're considering your portfolio allocation, remember to consider whether your human capital behaves more like a stock or a bond, and diversify your portfolio against it accordingly.