In order to maintain interest in an exercise, it helps to have a goal in mind. Whether that training goal is to win the Olympics or to look better in a particular tank top, the way it affects one's training is identical. A goal, no matter how large- or small-scale gives you a constant reason to exercise, even when it's inconvenient to do so. When it's more humid outside than you would like, or in the early hours of the morning, your goal will help you willingly get out the door and exercise. A friendly driver once pulled over beside me as I was running in the pouring rain to offer me a ride home. I was impressed with her concern, but I had never considered it an option to turn back early or stop my run on account of the rain. I had a road race to train for!