"When I wrote Lean In, some people argued that I did not spend enough time writing about the difficulties women face when they don't have a partner. They were right. I didn't get it. I didn't get how hard it is to succeed at work when you are overwhelmed at home. I wrote a chapter titled "Make Your Partner a Real Partner" about the importance of couples splitting child care and housework 50/50. Now I see how insensitive and unhelpful this was to so many single moms who live with 100/0. My understanding and expectation of what a family looks like has shifted closer to reality. Since the early 1970s, the number of single mothers in the United States has nearly doubled. Today almost 30 percent of families with children are headed by a single parent--84 percent of whom are women. I"