It is not bigotry to be certain we are right; but it is bigotry to be unable to imagine how we might possibly have gone wrong.
-- G.K. Chesterton
I smelled a rat the first time I read it. First of all it's contradictory: if you see a possible way you could be wrong, how can you be certain you're right?
Second, it isn't bigotry to be unable to imagine how you might be wrong. It might be thought nasty and unpleasant, but that's not the same thing. Bigotry is utter intolerance of any differing creed, belief, or opinion-- and being sure a belief is wrong doesn't necessarily mean you don't tolerate it. But then, the meaning of "tolerance" also gets confused. People think it means "allowing for the possibility that the other person could be right", when in fact tolerance is putting up with something you believe is wrong, because the evil that would come of trying to stop it is greater than the evil of allowing it. One has to make judgments about right and wrong, and judgments about greater and lesser evils, before it's even possible to be tolerant. A man of no conviction has nothing to tolerate.
But the main reason I suspected the quote was that it smacks of modern sentiment. I don't know if it could have been written by anyone in Chesterton's time (1874-1936), but it certainly couldn't have been written by Chesterton himself. It's too wishy-washy and obviously self-refuting, like, "There is no absolute truth," which is another thing our ancestors were too reasonable to say, at least in so many words.
And now I've unexpectedly found the real quote. I was listening to Alarms and Discursions (downloaded from librivox.org), and in Chapter 19, The Anarchist, I heard this:
No one worth calling a man allows his moods to change his convictions; but it is by moods that we understand other men's convictions. The bigot is not he who knows he is right; every sane man knows he is right. The bigot is he whose emotions and imagination are too cold and weak to feel how it is that other men go wrong.
"Too cold and weak to feel how it is that other men go wrong"-- now that makes sense, and that's Chesterton. To believe anything is to believe that others are wrong, but if you're a big enough person you can understand the lure of the wrong viewpoint and sympathize with those who hold it. Seldom do I meet anyone that sympathetic; I certainly have difficulty with it myself.
Update: The quote is completely correct-- check Oloryn in the comments. So, okay, I was wrong, but at least I was very passionate about it. :)
2nd Update (May 2012): I've had an epiphany! Yes, I was wrong about Chesterton being misquoted, but I was completely right about his meaning. When he says "it is bigotry to be unable to imagine how we might possibly have gone wrong," he means we need to understand how we might have come to the same incorrect conclusion as the person who disagrees with us (and who, we're certain, is wrong.)
To put it another way, Chesterton wasn't saying we have to be able to imagine that our belief is wrong. We just have to understand how we could have arrived at a different belief, the belief which we know is wrong, but which nevertheless is held as true by many other (misguided) people.
So we don't have to be in doubt of our own conclusions; we just have to be understanding about others' conclusions.
"We might possibly have gone wrong" doesn't mean our current conclusion is possibly wrong. It means that in an alternate universe, we could have come to the wrong conclusion.
To put it a fifth way, both those quotes of Chesterton's are saying exactly the same thing.
All is reconciled. Whew!