The moral of the story "The Tortoise and the Hare" is that the weakest opponent should never be underestimated. In the story, the rabbit is beat by the turtle in a race because he took a nap and underestimated the turtle's ability to pass him up.
Sometimes the moral of this story is that "slow and steady" wins the race. This can be applied to situations in which people are in a rush to do something — lose weight, get a promotion and so on — but slow and steady can get better results than going a faster pace towards one's goals. For instance, slow weight loss can mean that the person keeps the weight off longer.