Why?

There is an interesting phenomen I'll never understand: running for 26.2 miles in one day. Today is the Chicago marathon, a day where 45,000 people gather in an anxiety-provoking crowd, and run until their lungs are ready to explode. Today was a beautiful day, but no one looked like they were enjoying the elements. I saw people limping or on the ground with ice on their knees. What about this alleged "runner's high?" I didn't see the runners high-fiving each other, or saying, "dude, I totally felt amazing after mile 17."

So my question is, why do they do this to themselves? Mike and I enjoyed the day walking around and getting a hot dog. Sure, I don't have the bragging rights of running a marathon, but I don't have a swollen knee either.