'Thorn' in the Bible

Other seed fell among thorns, and the thorns came up and choked it, and it yielded no grain.

Because of the surpassing greatness and extraordinary nature of the revelations [which I received from God], for this reason, to keep me from thinking of myself as important, a thorn in the flesh was given to me, a messenger of Satan, to torment and harass me—to keep me from exalting myself!