Keeping your goal during a race

I find that keeping my goal in perspective is quite difficult and challenging during a race. Usually it's the body that tend to derail your plan, when you are struggling during a run due to fatigue, your mind cannot focus on the task at hand. Your body will keep telling you that your temperature level is too high, this is what happen to me during the recent 2xu run. I kept being afraid that I will end up slowing down too much later if I maintain a faster pace early or midway through the race. So I ran with so much apprehension that I keep holding myself back. I must try to overcome this problem this Sunday at the 350 half marathon.