Pushing Through

Why is it that at mile three I am beat down but I push on and at mile four I am revived and ready to go on. I push through and the next thing I know is I am at mile ten and my workout is done! However, put me on my knees to pray and I cant get past a few minutes. I try to push through and it is so dang hard. The rewards are so much more than that of ten miles and yet its so hard to press through to the thrown room!! Am I alone in this??