It might have been some project at work, or some project around your house. About half-way through the project you began to think that you would never finish. Perhaps it was taking much longer than you thought, which is not unusual. Perhaps you began to rationalize and even develop arguments for why you shouldn't finish. Maybe you even began to think that it wasn't God's will that you finish.
Many people fail to complete many things because of that kind of fatigue and discouragement.
This is especially true when things are going wrong in the process. When you knock the paint over, or break the glass, or blow up the microwave you are trying to install, it can be discouraging. This is especially true when you are tired physically. Frustration Frustration is another reason why we become discouraged. They became discouraged because they were so frustrated with the situation.