The problem with running

The problem with running is that you are never done.  I promised myself that if I ran a 3:10 marathon or faster, I would be perfectly content and never run another marathon.  If I hadn't run the goal time, I would've been unhappy and had to run another one to prove I could do it.  But now that I did it, I am wondering how much faster I could go. Maybe if I do this or that differently in my training....alas.  It is an endless cycle.  You think I would have learned that by now.  So be warned, once you start running you will never be able to stop!