To study or not to study?

Everyone loves that overwhelming sense of accomplishment when you've learned the material, studied hard, and done well on a test. But what about that dense, crushing feeling when you've studied just as hard, and didn't do so well? Did you simply not know the material as well as you thought? Did you completely blank out when it was show time? Or did you merely underestimate the amount of studying that was needed to do a good job? Then there are those people who never study and still manage to get A's. It is extremely hard to not get jealous when you're listening to a friend brag about how they went the entire semester without cracking open a book and managed to aced the class. Are these people any smarter than those that have to spend hours preparing for an exam? Do they just possess better retention skills? Or are they really just that lucky? I feel that this simply shows that each student, as well as his or her academic potential, is different and it's up to you to figure what it takes for you to fulfill yours and if you're willing to do the work (or lack thereof) involved.