Some Days You Have It and Some Days You Don't......It Happens!
I don't know why one day you can feel like crap on a run and another day you can feel great. What I do know is that you shouldn't let your mind prevent you from running. Tuesday if I had listened to my mind and not done my run I would have missed out on a great run! Your mind is a powerful thing and it can get the best of you if you let it. Some of my best workouts are workouts that I really didn't want to do.
Just get out and get it done. Not every workout will be the best but when you have a good one you'll feel amazing!