Certainty usually means you haven’t looked from the other side yet.

Total certainty is usually a sign of an unfinished job rather than a completed one. Once you have genuinely stood where the other person stands, you usually end up with a view that is still yours but has edges on it. The people with no doubts are often the ones who have only ever faced their own argument.

So do the swap out loud. Take something you are sure about and make the best case against it, properly, as though you had to win. You will either hold your view with better reasons or find it was thinner than it felt, and both are wins.