Then, for one reason or another, the economy slows down. Companies lay off employees and consumers are more careful about where they spend money, perhaps saving more than usual. As a result, the economy decelerates even further. If it slows enough, we have a recession.

During such a time, fewer people are buying homes. Even so, some homeowners find themselves in a situation where they must sell. Families grow beyond the capacity of the home, employees get relocated, and some may even find themselves unable to make their mortgage payment - perhaps because of a layoff in the family.