The person who asks what would change your mind has moved the discussion toward something testable.

Asking someone what would change their mind does something a hundred counterexamples cannot. It turns a contest of positions into a description of conditions, and once both people have named what would move them, the disagreement has an address and a size. It also reveals the cases where no answer exists, which is worth knowing early rather than after another hour.

Have the answer ready for your own views before someone asks. Name one observation that would change your position on something you hold firmly. If you cannot find one, you are not holding a conclusion so much as a commitment, and it helps to know which you have.