Paul had what he called “a thorn in his flesh.” He said that it was a messenger of Satan to keep him from exalting himself. We don’t know what it was. Some say it was his poor eye sight.

I’m sure you know your weakness. That thing that torments you, that keeps you from doing your best. But that weakness can be the very thing you can be glad about, because Christ will perfect His power through that weakness—so that we can be content with our weakness.

2 Cor 12:9-10

And He has said to me, “My grace is sufficient for you, for power is perfected in weakness.” Most gladly, therefore, I will rather boast about my weaknesses, so that the power of Christ may dwell in me. 10 Therefore I am well content with weaknesses, with insults, with distresses, with persecutions, with difficulties, for Christ’s sake; for when I am weak, then I am strong.