Start by identifying and understanding arguments against your position. After that, push yourself to come up with your own unique arguments against your positio

Start by identifying and understanding arguments against your position. After that, push yourself to come up with your own unique arguments against your position. Then take the time, which should be considerable, to have the debate with yourself backed up by data on both sides. Depending on how much time you devote to these exercises I’d guess this process should take on the order of months to years. After that you should be prepared to have a dispassionate discussion on the topic with your friend.