How could it be that Elisha requested a double portion of Eliyahu's spirit? The spirit is singular, so either he would receive Eliyahu's spirit or he wouldn't?
In the answer we learn that a student who internalizes his teacher's lessons and brings additional wisdom to bear on these lessons, cleaving to them and delving to their depths, can reach new strengths through these lessons that were previously unavailable to him.
This was the secret of Yosef's success. He constantly delved into his father's lessons, always kept his father's countenance foremost in his thoughts.
This is especially helpful to us who are each caught in our own spiritual slavery. We have to bind ourselves to the lessons of our Rabbis the teachings of our fathers, and even keep their faces fresh in our memory, and may it be HaShem's Will that, like Yosef HaTzaddik, we will be sped from the darkness of the pit to the spotlight of the King's attention.