Mercy can travel through wounds

Paul does not write this as a theory. Four verses later he tells you what he is drawing on: in Asia he was "so utterly burdened beyond our strength that we despaired of life itself."
That is the man saying God comforts us in all our affliction so that we may comfort others. The comfort he hands on is not general goodwill; it is the specific thing he received in the specific place he nearly did not survive. Which is why the mercy travels through the wound rather than around it. What you can give someone is shaped by what you needed and were given.
Scripture links:
- 2 Corinthians 1:3-4 - "the Father of mercies and God of all comfort, who comforts us in all our affliction, so that we may be able to comfort those who are in any affliction, with the comfort with which we ourselves are comforted by God."
- 2 Corinthians 1:8 - "we were so utterly burdened beyond our strength that we despaired of life itself."
The place you were most helped is the place you can most help.