There will be good days and bad days. There will be great runs and tough runs. Heck, there will even be days with no runs!
The point is, fitness it a journey not a destination. You can either live on a perpetual diet, or you can live a healthy lifestyle. I choose the latter because that means I don't have to start over. I just have to understand that pizza, chips and birthday cake are part of real life. I don't have to start over when I eat them. I can just enjoy the treat and go right back to my healthy life style following the last bite.
That's a good feeling.