When Leonardo da Vinci was painting the "Last Supper," he had an intense, bitter argument with a fellow painter. Leonardo was so enraged that he decided to paint the face of his enemy into the face of Judas. That way the hated painter's face would be preserved for ages in the face of the betraying disciple. When Leonardo finished Judas, everyone easily recognized the face of the painter with whom Leonardo quarreled.
Leonardo continued to work on the painting. But as much as he tried, he could not paint the face of Christ. Something was holding him back.
Leonardo decided his hatred toward his fellow painter was the problem. So he worked through his hatred by repainting Judas' face, replacing the image of his fellow painter with another face. Only then was he able to paint Jesus' face and complete the masterpiece.