Maybe Not

I had a good 9 miles today and I hurt the last 3.5 or so. I was looking to run a strong 13 the whole way but couldn't pull it off today. I knew it would hurt when I added miles and kept the pace up so I should not be too surprised. I heard the usual you went too fast comments. This is just the way I do it and it hurts until I adapt to the speed. Maybe I am crazy but maybe I'm not...