"We run, not because we think it is doing us good, but because we enjoy it and cannot help ourselves...The more restricted our society and work become, the more necessary it will be to find some outlet for this craving for freedom.  No one can say, 'You must not run faster than this, or hump higher than that.'  The human spirit is indomitable." Sir Roger Bannister

Running is freedom, which is a great way of looking at it. There are those days when you just feel drained from a long day of work and deadlines and you can't seem to muster up the confidence to get a run in.  I suggest going anyway. Because you can create energy by burning energy. Running will give you energy and a sense of freedom.  A freedom where you can escape your daily stresses, you'll find yourself cleansed and recharged after such a run. Even though just an hour before you felt like you couldn't do it.