Many investors' exposure to the stock market has grown larger over the past couple of years. Photo by Michael M. Santiago/Getty Images

There are very few absolutes when it comes to the timing of investment shifts, and that is because timing the market has proven to be a very inexact science. Yet, today, I am saying it is time to lighten up on some risk in portfolios . How do these statements reconcile?

The reason is that sometimes timing is just rebalancing and many investors’ exposure to the stock market has grown larger over the past couple of years. Along with this increased exposure to stocks, the market has become more expensive, which historically means there is greater risk in investing in the stock market today than in most periods.

Combine a higher weight in stocks and a hi

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