I made mentioned of this previously but the chart below from The Capital Speculator shows clearly exactly the point. For all the rejoicing about the great US stock gains this year, its actually a very unique case. The vast majority of all asset classes have fallen by quite a bit this year, very few are doing well at all.
Even assets such as emerging market stocks, bonds, and etc, are not just performing worse than the US stocks, they're actually red for the year. Its an incredible disconnect between US stocks and well...everything else. And as most people know, outliers tend to revert to the mean eventually.
Even within US stocks, there is a huge split between various assets. For example, tech has been doing very poorly vs the rest of the sectors.