She bases this on the Harvard Grant Study, the longest longitudinal study ever conducted.
Emotional contagion — or the psychological phenomenon where people "catch" feelings from one another like they would a cold — helps explain why.
Research shows that if your friend is happy, that brightness will infect you; if she's sad, that gloominess will transfer as well.
Children in high-conflict families, whether intact or divorced, tend to fare worse than children of parents that get along, according to a University of Illinois study review.
Robert Hughes Jr., professor and head of the Department of Human and Community Development at the University of Illinois and the study review author, also notes that some studies have found children in nonconflictual single-parent families fare better than children in conflictual two-parent families.
What's more, the "intensive mothering" or "helicopter parenting" approach can backfire.
"Mothers' stress, especially when mothers are stressed because of the juggling with work and trying to find time with kids, that may actually be affecting their kids poorly," study coauthor and Bowling Green State University sociologist Kei Nomaguchi told The Post.
"And so they're absolved of not only the work, but of learning that work has to be done and that each one of us must contribute for the betterment of the whole," she said.
Lythcott-Haims believes kids raised on chores go on to become employees who collaborate well with their coworkers, are more empathetic because they know firsthand what struggling looks like, and are able to take on tasks independently.
Those with limited social skills also had a higher chance of getting arrested, binge drinking, and applying for public housing.
"This study shows that helping children develop social and emotional skills is one of the most important things we can do to prepare them for a healthy future," said Kristin Schubert, program director at the Robert Wood Johnson Foundation, which funded the research, in a release.
"This suggests that investments in early parent-child relationships may result in long-term returns that accumulate across individuals' lives," coauthor and University of Minnesota psychologist Lee Raby said in an interview.