Buffalo Marathon DNF (Did Not Finish)

Did not run for two full weeks due to injury of right knee and right achilles. Last minute I decided to make the trip because my flight was non-refundable and I figured I would just run the half marathon. Started off slow with no pain in achilles but slight pain in right knee.
10K 54:00
1/2 marathon 1:54:00
Instead of stopping halfway like I had originally intended.. I decided to run the full because I had traveled all that way and I figured I could check another state off the list of 50. Picked up the pace and began to pick people off one by one. Passed 14 people from mile 13 - 15. Finally caught up with a guy from Atlanta @ 17.5 and ran with him until 23. Pain grew to a new level @ 23 and I decided to stop and sit... time 3:31:00. Bad idea as I was unable to start again. Picked any excuse from the list of hurt knee, hadn't run in two weeks, hotel check-out time was approaching, etc... and bowed out of the race. Regrets? Well, upon reflecting I sort of wish that I had at least walked the final 3 miles to get a medal but I am at peace with my decision because had I never stopped then I would never know that I never want to feel this way again about a finish to a race. I will remeber this plane ride home from Buffalo for a future race when things get tough and I feel like quitting. Race, walk, or crawl to finish no matter how long it takes.