Leaders are people who lead by example. So, if a subordinate is not able to do a task, he or she can demonstrate how the job should be done by doing it single-handedly. These people lead by their virtuous traits in personal behaviour,earn respect by respecting others, know how and when to delegate responsibility, ensure commensurate authority is given to subordinates along with responsibility and so on.
Mangers, on the other hand, just know how to get the job done by efficiently managing people under him or her and rationally utilising the available resources.