2 Cor. 12:7-10 "To keep me from becoming conceited because of these surpassingly great revelations, there was given me a thorn in my flesh, a messenger of Satan, to torment me. Three times I pleaded with the Lord to take it away from me. But he said to me, "My grace is sufficient for you, for my power is made perfect in weakness." Therefore I will boast all the more gladly about my weaknesses, so that Christ's power may rest on me. That is why, for Christ's sake, I delight in weaknesses, in insults, in hardships, in persecutions, in difficulties. For when I am weak, then I am strong."
"It's not always God's will that you be healed. It's not always the Father's plan to relieve the pressure. Our happiness is not God's chief aim. He doesn't have a wonderful (meaning "comfortable") plan for everybody's life-not from a human perspective. Often His plan is nowhere near wonderful. As with Saul, His answer is not what we prayed and hoped for. But, remembering that He is forming us more and more into the image of His Son, it helps us understand His answer is based on His long-range plan, not our immediate relief."
(Chuck Swindoll, Paul: A Man of Grace and Grit)