Debbie Ford suggests a good inquiry:
Go back to a situation where you experienced a good deal of stress, and that is still not resolved.
Then ask yourself: What do I have to let go of to find peace with it?
For me, the general answer seems to be everything I think I know.
And then there are some more specific answers, such as being right, or seeing my view as right. Seeing the other person as wrong. Wanting the world to conform to my ideas.
As with any inquiry, it is very helpful to allow this to sink it, to be processed by our whole being - body, feelings, mind and beyond. To take time with it.