Thorn in the flesh: When we are weak, then we are strong.

Therefore, in order to keep me from becoming conceited, I was given a thorn in my flesh, a messenger of Satan, to torment me. Three times I pleaded with the Lord to take it away from me. 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 about my weaknesses, so that Christ’s power may rest on me. That is why, for Christ’s sake, I delight in weaknesses, in insults, in hardships, in persecutions, in difficulties. For when I am weak, then I am strong. (2 Corinthians 12:7-10)

The Achilles heal of strength  

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Strengths breed pride.  "Pride comes before the fall" is a cliche for a reason.  When we lead solely based on our strengths, then we are operating solely by our strength.  Thus our strength is constrained by the limitations of humankind.  We weary, we lose focus, we burn out, and we have questionable motives.  Worse, we are more prone to sin with our strengths than our weaknesses if they come out of balance due to misuse and abuse.  Strengths often lead to loneliness in one way or another.  

Weaknesses breed humility.  When we recognize that our weakness, our "thorn,"
 prevents us from accomplishing the task we are called to, then we are forced to rely on the strength of others.  Humility allows us to call for reinforcements and teamwork to tackle a project.  Humility allows us to call to Christ Jesus (who lives within us!) to work through us to resist temptation and overcome the evil one by his unlimited strength.

Weaknesses help us.  Do you fire the business manager whose strategy just cost the company thousands? Or do you leverage that "training" for their next project?  We often learn more from our mistakes than our failures.  It is difficult to see who we have become, who God as has made us, without the our "thorn" and the trials we've endured.  

Weaknesses help others.  Just as explorers hire experienced Sherpas who've been over the mountain before, so do individuals struggling with pain and/or sin desire experienced guides who've been through the valley of the shadow of death.  People seek others who share their "thorn," someone who understands their plight and has experienced God's grace through it all.