Tom Morris calls the following "The Seven C's of Success": a clear conception of what we want, a strong confidence that we can attain that goal, concentration on what it will take to achieve it, consistent pursuit of our goal, an emotional commitment to the value of our goal, good character that guides us along the way, and a capacity to enjoy the process.
The second C of success, according to Morris, is a strong confidence that we can attain our goal. As C.S. Lewis puts it,
Very often the only way to get a quality in reality is to start behaving as if you had it already.
Morris is not arguing that we can do anything we put our minds to, nor that if we just believe we can achieve. Rather, he advises us to choose goals or projects for which success is a real possibility. Our goals may still be very challenging, but in some important sense they are still realistic. Given this, we can reasonably cultivate an inner attitude of confidence, which will help us not only pursue but achieve the goals in question.
While such confidence in ourselves is not required for success–we may just get lucky, after all–it has an important role to play. As Morris notes,
A strong confidence is no guarantee of success. But it is among the chief facilitators of it.
Confidence facilitates success because it helps us to persist and persevere through difficulties, reminds us that we chose the goal we are pursuing because it is within our grasp, and enables us to tap into the gifts and abilities that we possess. It may also help us discover new ones along the way, which can further boost our confidence.
The above is drawn from Tom's entertaining and enlightening book, Philosophy for Dummies.