What: The ability of humans, when faced with data that contradicts what they believe to be true, to restructure their world around that contradiction.

Why: When your belief is contradicted, the right-thinking thing (or, more accurately, the left-thinking thing) is to revise your belief. But most people can't or won't do that quickly. We become attached to what we believe. We live in a time when truth changes every day—when more things have been invented in the past century than all the centuries previous—and we can't keep up. And so we do an amazing thing: We create unique inter-worlds in our heads, states that are not quite in line with what we knew and not quite in line with what we now know. Those states take many names: faith, rebellion, nostalgia. We often hold on to it as long as possible, before the new truth overwashes us. It can be addictive to stay there. Like with everything else, too much dissonance can be harmful.

Impact: Usually we view this state as negative. Let me see if I can put you in a dissonant state in a positive way. Ready to perform a psych experiment on yourself? Okay, watch this Dschinghis Khan clip from the 1979 Eurovision contest:

If you don't speak German, you have no idea what you just heard. I can fix that. Click on this video with English "subtitles" (apologies for some coarse language):

See, now you know exactly what they're singing. Sure, your rationality tells you that they're not saying, "Billy is a handyman/Porcelain is the surest plan." Doesn't matter. You're in a state of cognitive dissonance, with your brain constantly repeating the catchy lyrics you instinctively know to be accurate. About the only way to get out of this state is to subject yourself to the absolute truth: Dschinghis Khan singing "Moskau" in English. But do you really want to?

Personal Connection: I got the idea for this Most Beautiful Thing by talking to a pastor who believes critical thinking is the best way to approach faith. Most people, I think, would view cognitive dissonance as a bad thing, pointing to all the terrible things fanatical people have done. I call it proof that we've evolved far beyond anything else on the planet. I have trouble believing in truth, because I know that a mere evolutionary eyeblink ago, people just as strongly believed the world was flat, demons made people sick, and humans couldn't fly. But my brain conspires to make me believe in something. So why not what I want to believe?

Other Contenders: scientific experimentation, and seriously, did you really imagine that Diet Coke was safe?; sublimation into art, as Pablo Picasso shows when confronted with the spread of Nazism; public protest, and I think I just guaranteed that a number of people will click on every link I post.