All of us, even the children, know how painful a thorn can be, and a thorn in a sensitive area, like under a fingernail, can be extremely painful, a nagging pain that never lets you mind completely focus. Some have suggested he suffered from migraines, or malaria, epilepsy, a severe speech impediment. Others think his pain was not physical but mental, as with bouts of despair or depression. I do not know his particular thorn. I also know that all of these things come not from God, but are, as Paul said, messengers from the evil one.
Evil is real and has power.
It has touched the lives of everyone here. Paul prayed at least three times for this pain to be taken away from him. Like all of us, Paul was not only ready to pray to God, but also to tell God what the proper answer should be. God does not answer our prayers in the way we expect, and not here in the way Paul expected. My grace is sufficient for you, for my power is made perfect in weakness.