One Reason Why It Is So Important to Set Goals

One reason why it is so important to set goals and subgoals far in advance is that

A) people consistently underestimate how long a task will take.
B) once you have stated the goal, you don't have to think about it any more.
C) if you have a clear goal, you won't have to work as hard.
D) most people underestimate their skills, so a goal provides encouragement.