S&P 500 had a total return

But that is known only with hindsight.
With diversification, you have to commit yourself in advance to
the fact that a variety of securities in your portfolio will move in
different directions or at different paces. The simple 50–50 split of
this example is diversification, but you can do a lot more.
The result of diversification is not always a smaller loss. It can
be a smaller gain. In 2003, the year the stock market began its recovery
from the 2000 crash, the S&P 500 had a total return of
28.7 percent while the return for the Russell 2000 was a stunning
47.3 percent. The combined return was 38 percent.