2 Corinthians 12:7

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.

(v7, NIV)

Paul was given this thorn in his flesh in order to keep him from becoming conceited. Paul has much to boast in, and God has blessed him with these things. However, God didn't make Paul perfect. God made Paul the way he intended to make him. In making him, God gave Paul some imperfections.

For all have sinned and fall short of the glory of God

(Romans 3:23, NIV)

Though we should desire to be perfect and desire the things of God, we know that we fall short. We aren't perfect, nobody's perfect. However, it is not wrong to desire to better ourselves in certain ways. Yet, as we get better and better in whatever way, there is always an opportunity for us to become conceited. We are tempted to boast in ourselves, in how good we are or how cool we are or whatever it may be. God gives us weaknesses. In these weaknesses we are humbled. In these weaknesses God's power is made perfect. God is so good.