Many marathon runners face a difficult problem in the latter stages of the race... that is when they hit the wall. This refers to depleting their glycogen (glucose, stored in the liver and muscles)and the feelings of fatigue and negativity that come with it. It is the most readily available fuel source to burn when exercising, so our bodies prefer it. When we run low on glycogen, our muscles hurt and our brain wants to shut down activity as a preservation method... this may lead to negative thinking, forgetting the big picture. Most people come to the Lord for the same reason... the easy answers stop coming. Also it is not uncommon for people who serve God to hit the wall from time to time. God excels when the easy way is not available.