In the minds of most men, the kingdom of opinion is divided into three territories,—the territory of yes, the territory of no, and a broad, unexplored middle ground of doubt.

Most of what you believe sits in a large middle region you have never examined, between the few things you are sure of and the few you have ruled out. The yes and no territories feel like the whole map because they are the only parts you visit. The unexplored ground is where almost everything interesting lives, and it stays unexplored because doubt is uncomfortable to stand in for long.

Pick one question you have been treating as settled and deliberately return it to the undecided pile for a week. Read the best case against your position, made by someone who holds it seriously, before you decide again.