You know, many people don't realize that Paul dealt with a spirit that tried to oppress him.
2 Corinthians 12:1-13 English Standard Version (ESV)
1 I must go on boasting. Though there is nothing to be gained by it, I will go on to visions and revelations of the Lord. 2 I know a man in Christ who fourteen years ago was caught up to the third heaven—whether in the body or out of the body I do not know, God knows. 3 And I know that this man was caught up into paradise—whether in the body or out of the body I do not know, God knows— 4 and he heard things that cannot be told, which man may not utter. 5 On behalf of this man I will boast, but on my own behalf I will not boast, except of my weaknesses— 6 though if I should wish to boast, I would not be a fool, for I would be speaking the truth; but I refrain from it, so that no one may think more of me than he sees in me or hears from me. 7 So to keep me from becoming conceited because of the surpassing greatness of the revelations, a thorn was given me in the flesh, a messenger of Satan to harass me, to keep me from becoming conceited. 8 Three times I pleaded with the Lord about this, that it should leave me. 9 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 of my weaknesses, so that the power of Christ may rest upon me. 10 For the sake of Christ, then, I am content with weaknesses, insults, hardships, persecutions, and calamities. For when I am weak, then I am strong.
This spirit tried to exploit Paul's human weaknesses with temptations, inspire insults from the opposition, orchestrate hardships of circumstance, inspire persecutions, and it even use its power to bring about natural calamities... all in the hopes of crushing Paul's resolve to preach the Gospel.
Paul prayed three times for this spirit to be removed. But God allowed it to remain because in all these things, it kept Paul humble and dependent upon the grace of Christ.