Every 90 days I lie in a whirling CT machine, dye coursing through my veins, and the doctors look to see whether the tumors in my liver are growing. If they are not, the doctors smile and schedule another scan. The rhythm has been the same since my doctors told me I had stage IV colon cancer two and a half years ago. I live for three months, take a deep breath and hope to start over again. I will probably do this for the rest of my life. Whatever that means.

But in the weeks after I learned that the breast cancer I have been in treatment for over the past year had spread to my bones — breaking my spine and becoming incurable and most likely fatal — finding the perfect living-room couch has begun to feel like the most important thing I’ve ever done.

Let us consider me as a test case. As I have said, I would like to die peacefully with Thomas Tallis on my iPod before the disease takes me over and I hope that will not be for quite some time to come, because if I knew that I could die at any time I wanted, then suddenly every day would be as precious as a million pounds. If I knew that I could die, I would live. My life, my death, my choice.

I began to realize that coming face to face with my own mortality, in a sense, had changed both nothing and everything. Before my cancer was diagnosed, I knew that someday I would die, but I didn’t know when. After the diagnosis, I knew that someday I would die, but I didn’t know when. But now I knew it acutely. The problem wasn’t really a scientific one. The fact of death is unsettling. Yet there is no other way to live.

When Jeff Zaslow's column appeared in the Wall Street Journal (WSJ), about a dozen publishers emailed me, asked if I would be willing to write a book based on it. (I found this laughable, since at the time the palliative chemo was not yet working, and I thought I was down to about 6 weeks of good health). When the palliative chemo started working and we had some breathing room, I mentioned this to Jai, and she told me she wanted to do it. She was, in fact, quite emphatic. We had always talked about my "writing the manual" for her and the kids in my remaining time, and Jai felt that if it were a "real" project, I might take it much more seriously.

I am flattered and embarassed by all the recent attention to my "Last Lecture." I am told that, including abridged versions, over six million people have viewed the lecture online. The lecture really was for my kids, but if others are finding value in it, that is wonderful. But rest assured; I'm hardly unique. Send your kids to Carnegie Mellon and the other professors here will teach them valuable life lessons long after I'm gone.

Today is a pretty important day. It was August 15th, 2007, when I was told I likely had "three to six months of good health left." Today is six months from that day. Just to prove I'm still alive, here I am, holding today's New York Times! I rode my bike today; the cumulative effects of the chemotherapy are hurting my stamina some, but I bet I can still run a quarter mile faster than most Americans. The doctors weren't wrong; they always said that if the palliative chemo worked, I'd buy more time, but that it was a long shot. And the doctors have done a brilliant job of tweaking my regimen to help my odds. How much longer this will work is hard to know, but I'm going to keep having fun every day I have left, no matter how many or how few of them I get.

Shortly after my terminal diagnosis, I knew that one of my biggest priorities was to create memories for my children. Chloe and Logan are both so young that it's likely they'll have no direct memories of me. Dylan is the oldest, and at 5 (turns 6 in December), his memories are likely to be fuzzy. Hence the engineering question: What would make for the sharpest, most visceral memory, esp. for a kid who loves animals? Answer: go for a Dolphin Swim!