What is earnest is not always true on the contrary, error is often more earnest than truth.

Sincerity is not evidence. People who are wrong frequently hold a position with more heat than people who are right, partly because a shaky belief needs conviction to prop it up while an accurate one can afford to be stated quietly. Intensity tells you how much somebody cares, not whether they are correct.

That applies to your own beliefs as much as anyone else’s. When you notice you are arguing with unusual force, check whether the force comes from the evidence or from what it would cost you to be wrong. Strong feeling is worth examining rather than trusting.