Our sufferings may not be due to specific sins we have done, but may be ministers to our benefit. And we know that all things work together for good to them that love God, to them who are the called according to his purpose. The thorns hurt but they serve a useful purpose. The purpose was to prevent spiritual pride. It was better to prevent it rather than try to handle the problems it would cause.
Nothing is so treacherous in the Christian walk as spiritual pride.
Look out if you have unusual spiritual gifts. Look out if you have unusual opportunities. Look out if you have been blessed greatly. Look out if you have great talents and abilities. Paul was susceptible to pride.