Why run a marathon?

For over 20 years I have been running for recreation and fitness, anywhere from about .8 to three or four times a week for distances of 4 to 6 miles. I have rarely been concerned about performance or proving anything. I was in it for fun and fitness. Suddenly, at age 50, I am signed up for the Philadelphia Marathon on November 23, 2008, and training seriously. How did this happen?
The influence of a running-fanatic friend was a factor. He encouraged me to try a half-marathon organized by the New York Road Runners back in January. This was the longest distance I had ever run and I was not properly trained for it. I was sore as hell for days afterwards, but I loved it. Five thousand pairs of feet trotting through the cold air of Central Park, a kin-hin line writ extremely large. I decided I would meet the NYYR requirement for entry into the New York Marathon in 2009 by running in at least nine races in 2008, and thus open the option of doing a marathon.
Then my running friend got into my head again: Why don’t you do Philadelphia in the fall? It’s open to anyone who pays the registration fee. I thought this over for a couple weeks, fretting over the difficulty of fitting training into an already busy life. Then just said fuck it, hit the website and did the deed.
Now I am embarked on a formal training program (from the Running Planet) that prepares you to complete a marathon in four hours. I felt irrationally attached to the four hour number even before arriving at it rationally. It’s a nice round figure, and four hours of continuous running is quite enough, thank you, so let’s get it over with. It’s a fortunate coincidence that my running history is such that the four hour goal does appear to be reasonable and attainable. So I am going at it five or six days a week, getting up before dawn to trod the pavement and run around Liberty State Park as the sun comes up, hitting the treadmill at work, exerting myself like never before in my life.
Why do this? I have long been vaguely curious about the experience of completing a marathon and thought it might be interesting to try it some day and find out if I could do it. Then I noticed I was 50 years old. Now seems like a pretty good time to get started, rather than waiting until 60 or 70.
Yes, but that’s doesn’t answer the question: why do this? I read some place that there are as many reasons as there are runners, but that’s another evasion.
Am I trying to outrun the grim reaper? Well, no, I fully expect to die. But first I would like to run a marathon.
But why? Am I trying to prove that I am disciplined and tough? Maybe a little. I don’t think I need to prove that I am fit, it’s a pretty simple and uncontroversial fact. But I will rather enjoy showing my medal to people. I guess that would be about ego gratification.
Why? Why go to so much trouble for ego gratification, or whatever it is? I don’t know. Yesterday I was in Urban Athletics buying gear, and had a chat with one of the co-owners. When I raised this question with him, he simply said, cross the finish line and you’ll know why.
I am reminded of something my Zen teacher once said to me: Ultimate truth cannot be known. But it can be experienced. Perhaps Jerry from Urban Athletics was saying the same thing.
Update: A few days later, Sensei was not impressed when I told him this story about the above remark from the guy at Urban Athletics. Ever the consummate Zen dude, he said: why ask why?