This is a “two-tier recovery,” said Matthew Mish, head of credit strategy at the investment bank UBS. About 60 percent of Americans have benefited financially, he said, while 40 percent have not.

The 40 percent — which Mish calls the “lower tier” — have seen paltry or volatile wage growth, rising expenses for housing, health care and education, and increased levels of personal debt. They tend not to own homes or many stocks.

In discussions with 30 Americans unable to pay all of their bills, a clear pattern emerged: Most were able to eke by until they faced an unexpected crisis such as a job loss, cancer, car trouble or storm damage.

The extra expense caused them to get behind on their bills, and they never fully rebounded.

Economists fear such precarious financial situations put many Americans at risk if there is even a mild setback in the economy, potentially setting up the next recession to be worse than anything in recent history except the Great Recession.