Guilt management can be just as important as time management for mothers.

I'd worked on leprosy and malaria in India [at the World Bank] and asked myself the question: Why do we let 2 million children die every year around the world for not having clean water? Because they're faceless and nameless. So, for me, Facebook looked like it was going to solve the problem of the invisible victim.

Your life's course will not be determined by doing the things that you are certain you can do. Those are the easy things. It will be determined by whether you try the things that are hard.

I was grateful that Facebook already had generous bereavement policies . Now Facebook employees receive 20 days paid leave to grieve the loss of an immediate family member and 10 days for an extended family member. I'm proud that we're able to do this and I hope more businesses do the same. Only 60 percent of private sector workers get paid time off after the death of a loved one, and then it's usually just a few days. Workers and families deserve better than that.

But the upside of painful knowledge is so much greater than the downside of blissful ignorance.

Men feel like they can be a professional and a father. For women it's "or." That's offensive to me. The concept that it's not possible is crazy.

I have never met a woman, or man, who stated emphatically, "Yes, I have it all.'" Because no matter what any of us has—and how grateful we are for what we have—no one has it all.