About 20 years ago I ran across a study of homeless people in NYC. It turned out that a lot had lead comfortable middle class lives, and like most of us with the resources to handle one economic setback. Then two things went wrong. The first drained their reserves, the second put them on the street.

A particularly common combination was a health problem followed by foreclosure.

It has been 20 years, but I have seen no reason to doubt that the same pattern would be largely true today.