Running in a state of despair

I ran the Standard Chartered Marathon - the whole of 42.195km. It's my 3rd time running it. Having went through the experience before, I thought I would know how to survive the race this time round. But it wasn't meant to be.

I ran well for the 1st 2 hours, before I hit the 'wall'. My legs started giving way, my thighs started cramping and I started walking. From my initial target of completion time of 5 hrs, I had it changed to 7hr 30min. I figured that if I walked the remaining part of my race, that should do the trick. My final result - 6 hrs.

The point here - my mind was playing tricks on me. The pain got to my head. I succumbed to pressure and allowed the environment and my body to lead me. Where are my goals in life? Am I so lost that I have no motivation to give my best for the race? Am I a person who only have big dreams, but no follow-ups to fulfil those thoughts?