Every year on Sept. 11, I'm like every other American. I think about that awful day. I think about the 2,980 people who died, and I think about the countless lives that were shattered, and I think about the ash and the smoke and the falling man.

I make sure to take some time to think about the hopeful things too, the courage displayed, the first responders rushing into danger, the friends and family holding each other tight, the way people came together, the countless heroes like my friend Jason Kander, who volunteered that day to change his life in order to protect Americans. I think about Yankee Stadium after Derek Jeter hit a famous home run just a few weeks later, and how everybody sang "New York, New York," over and over and over, nobody wanting to leave, nobody wanting to break that circle of love and strength.

And always before the day is done, I find myself thinking about a little girl named Christina Green.

She would have been 17 years old today, on 9/11.

On Jan. 8, 2011 -- it was my birthday, I was 44 years old -- I flew to Phoenix for the BCS Championship Game between Oregon and Auburn. It was a Saturday; the game was two days later. On my layover in Minneapolis, I heard that there had been a shooting in Tucson, and that a Congresswoman named Gabrielle Giffords had been wounded. I'm not sure that the name meant anything to me. By the time I got to Phoenix, it was late and dark and I was exhausted. I went to bed without thinking much about the shooting or anything else.

It was sometime early the next morning -- it was still dark, I remember that -- that I read that a young girl named Christina Green had been shot and killed. I read that she had asked a neighbor to take her to the rally because Christina loved Gabby Giffords and maybe wanted to become a politician one day. I read that Christina was the daughter of Dodgers scout John Green, and the granddaughter of the famed baseball man Dallas Green. I read that she was the only girl on her Little League team.

But I think it was when I saw that she was born on 9/11 that I started to cry uncontrollably. It was one of those horrifying and overwhelming cries where I sobbed and sobbed and then it seemed to be over and then I started crying again. I had not cried like that since I was a little boy. I have not cried like that since.

Why did I cry like that? I don't know why, not really. I did not know Christina. I did not know her family. Surely, it had something to do with our oldest daughter, Elizabeth, who was born on 8/30, just 12 days before 9/11. I know it had something to do with our own personal 9/11 experience. We were home, our first home. We saw the buildings collapse. We raced into the nursery. Elizabeth was sleeping. We picked her up and took turns holding her tight.

I know the crying had something to do with the horror of it all -- the horror of guns and killers and our apparent powerlessness or unwillingness to stop it -- and how none of that should have had anything to do with a 9-year-old girl who dreamed of helping people someday.

Then there was something else, something deeper, something opaque and painful and heartbreaking, something that even now I cannot explain.

I drove to Tucson to see the scene. I had to. I drove to the Safeway shopping center where the killings happened -- six dead, 19 injured, Gabby Giffords in a coma. Almost nobody was there. I don't know why I expected more. Most of the parking lot was blocked by yellow police tape. A couple of officers walked around the scene, but only a couple. A drugstore was open, and I saw a few people wander in and out of it. A father took photographs of his children at the scene. "Smile," he said to them.

I walked into a restaurant in the shopping center and ordered a sandwich. The owner thanked me for coming in. He worried that no one ever would again.

Then I went to Christina's school. It was a brick building, and in the moment looked identical to the school where our Elizabeth went (later, I realized, it was entirely different). There were ballet slippers and teddy bears and signs left there for Christina. I walked to the car and drove back to Phoenix in silence. I had not found what I was looking for. I don't know what I was looking for.

Elizabeth turned 17 about two weeks ago, because that's how it works, that's how time works;, it relentlessly marches on. There is some part of me, some part of us, that cannot accept time's insistence. I sometimes look at Elizabeth and am at a loss. I cannot believe that so many years have gone by. I cannot believe that she's come so far.

Today was one of those days.

"Can you believe I'm 17, Dad?" she said, out of nowhere as I dropped her off at school.

"No," I said. "I can't believe it."

She cackled -- she has learned how to cackle recently -- and she bounded out of the car and raced over to talk with some friends, and I watched them laugh happily. That's when I realized that today was 9/11, and that Christina Green would have been 17. I felt the tears coming again. I held them in and drove away.