“The first decade of the 21st century, and the second one that’s drawing to a close, have reinforced for investors some timeless market lessons: Returns can vary sharply from one period to another. Holding a broadly diversified portfolio can help smooth out the swings.”

In the article by Dimensional, we see two very different sets of returns for the last two decades. In the end, investors that had well diversified portfolios performed well and had good experiences.