Sheryl Sandberg, the COO of Facebook, gave the most personal speech of her career, publicly discussing for the first time the sudden death of her husband Dave just over a year earlier. She found him lying on the floor of a gym during a friend's birthday party in Mexico. She described the deep fog of grief — what she called 'the void' — an emptiness that fills your heart, your lungs, and constricts your ability to think or even to breathe. But she told the graduates that she also learned something profound: when life sucks you under, you can kick against the bottom, break the surface, and breathe again. The easy days ahead will be easy, she said. It's the hard days that will determine who you are.