Why do this?

Part of being a runner is having to deal with injury and self doubt.  In my case the two tend to come as a pair and at the worst time in my training.  Last week  I signed up for The 2012 Chicago Marathon while nursing both a calf and knee injury.  I do not run with knee pain, this is my one rule that I hope will save me from the scalpel later on. Not running for long periods of time makes me into another person.  I sit around and drink too much wine, eat for pleasure and dance the fine line of despair.  Emotionally I have been a wreck and committing to Chicago made me doubt myself even more.  The big question that keeps coming up is 'why am I doing this?'.  Training for a marathon is not an easy task to take on as a parent of 2 small babies and an active 9 year old.  My wife and I are already passing like ships in the night, so adding a training plan that will peak at around 75-80 miles a week, massage therapy, juicing, biking, swimming, core and flexibility work to the mix makes everything so much more difficult.  Why? 
This morning I put the why question to sleep.  As I woke at 4:30 for my morning tempo run I could feel myself returning to form.  My calf  is still tight and I will continue to work on this as we progress into the base phase.  My knee pain is gone and I am taking the proper precautions to avoid injuring myself again.  The balance has returned, and I am elated, even manic.  I have no choice but to set my goals for the year so high that I almost can not achieve them.  I am beyond excited to take on the Chicago Marathon.