Power made perfect in weakness

In 2 Corinthians St. Paul makes an abrupt change in chapter 10 from talking about a collection for the poor in Jerusalem to defending himself against some accusers.  He realizes, he says, that he may sound foolish, but he goes on about all the great and difficult things that he has done.  It is a powerful passage. 
Then in 12:7-10 he talks about "a thorn in his flesh" that he asked God to take away.  God's answer is a great help and challenge for me.  God says, "My grace is sufficient for you, for power is made perfect in weakness."  The "thorn in his flesh" that Paul is complaining about keeps Paul aware that all the good things he has accomplished were due not to his skill but to God's power at work in him. 
There's all kinds of guesses about what Paul's "thorn in the flesh" was.  In 10:1 he seems to be referring to what his critics say of him when he says, "....I who am humble when face to face with you, but bold toward you when I am away!"  Then in 10:10 he quotes his critics as saying, "His letters are weighty and strong, but his bodily presence is weak, and his speech contemptible." 
As I prayed over this passage, I found myself wondering if Paul's "thorn in the flesh" was stuttering.  It certainly would be frustrating and humbling if a man, who had so much to say and who could put it so powerfully in writing, had a serious speech impediment.  A "thorn" like that would easily make Paul keenly aware that all of his great accomplishments were God working through him.  So Paul concludes, "When I am weak, then I am strong."