Can a competent follower become a great leader?

Is it possible that someone can be merely technically competent at their job, and yet be able to inspire and motivate others when placed in a leadership position? Our instincts would say that such a transformation is highly unlikely. After all, why would anyone want to be led by someone who is not exceptional in everything they do?

History and logic, however, cast doubt on that assumption. Ulysses S. Grant was, at best, a marginal soldier. By all accounts he was an alcoholic who failed at nearly every thing he had ever done. Yet he became one of the most famous leaders of the 19th century. When placed in a position of leadership he inspired others, achieved results where others had failed, and accomplished arguably the most important military success in the history of our country. How could this happen?

To find the solution, perhaps we should change the context of the original question; “Have you ever known an exceptional employee who struggled or failed when placed in a leadership position?” If the answer to this question is yes, and we can agree that the degree of success does not necessarily correlate from one position to the other, then could it also be possible that a competent follower can become a great leader?