One of my fondest memories from high school is the Humanities course I took as an elective my junior year. Our instructor (who we called "Madame" because she was also the French teacher) didn't just introduce us to classic works of literature, art, and music; she gave us new ways to think about the world. One of her assignments seemed simple, maybe even silly, but it's had a lasting influence on my personal and professional life.
Our task was to write down the steps for assembling a peanut butter and jelly sandwich, in correct order and complete detail. On the date the paper was due, we arrived in class to find a table laid out with a loaf of bread, jars of peanut butter and jelly, plastic knives, and paper towels. Madame stood at the table and precisely followed the instructions as they were read aloud from each student's paper. Most 6-year-olds can assemble a sandwich, but when the job is broken down in such detail, it proves to be amazingly complicated. If you forget something as basic as removing a jar lid or the twist tie/tag that holds the bread bag closed, you go hungry. Student after student failed the task, but at least one succeeded. It was the best peanut butter and jelly sandwich that I have had in my entire life.
The true measure of a person's understanding of a process or idea is how well they can explain it to someone else. If you claim to know a song, you should be able to sing or play it for others. If you genuinely know what a word means, you should be able to define it clearly. If you really know how to operate a piece of machinery, you should be able to teach someone else to use it properly. Ideally, our beliefs would work the same way. If I'm asked why I believe in a given proposition, I should either be able to provide evidence for it or be prepared to change my mind when I'm presented with solid, objective evidence that supports a different position.
What's your most cherished belief, and could you explain it to someone who'd never heard of it before? If aliens landed on Earth, understanding science and logic and English and eager to grasp our culture, could you make a rational case for your ideas, or would you have to resort to appeals to authority and phrases like "That's just the way it is"? If the aliens didn't grasp your best explanations, where would the blame lie—with them, or with you? If you can examine your views as though they're completely new to you and still make sense of them, you've passed the test. If you tried but found your mind retreating to old and familiar territory, give yourself partial credit for the attempt. And if you tried and found that you had to discard a pet theory that hasn't stood the test of time, you've gone to the head of the class.