Science behind a happy relationship

Courtesy of Happify:

Study: two-parent families improve economic mobility

What is the most important factor blocking social mobility in the US? 
It could be single parents, not economic inequality.
 
As reported by New Scientist:

An important new Harvard study that looks at the best community data on [economic] mobility in America – released this past weekend – suggests a cause that progressives may find discomforting. ...

A lot of research – including new research from the Brookings Institution – has shown us that kids are more likely to climb the income ladder when they are raised by two, married parents. But this is the first study to show that lower-income kids from both single and married-parent families are more likely to succeed if they hail from a community with lots of two-parent families. ...

Economic inequality was not a statistically significant predictor of absolute or relative mobility.