Goal-setting simplifies and makes possible the attainment of a seemingly impossible dream. For example, it may seem unrealistic to say, "I want to run a marathon." However, it is feasible to say, "Tomorrow I will run 3 miles and Tuesday I will run 5 miles, until eventually I build up to the 26.1 miles." Eventually you will reach your goal, but the in-between steps are less grandiose and overwhelming.
The process of setting a goal also makes the possibility for success real because you are not only telling yourself, "This is what I want to do", but you also are telling other people, thereby making it concrete. By setting a goal publicly, you may increase your willingness to work through the tough times.
Goal-setting also aids in improving your focus on the important details that you need to address before achieving a goal. We are so busy, and it is so easy to lose focus or become distracted and focus on other responsibilities, thus abandoning our goals. However, by setting a goal and writing out the steps needed, you make your goal a priority.
Therefore, goal-setting puts the power in your hands to achieve an outcome you desire by focusing your attention, simplifying a seemingly large feat and by transforming some abstract wish into specific, daily, conquerable behaviors.