HT: Bob Prokop
From The City of God, Book II:
Even after the plain truth has been thoroughly demonstrated, so far as a person is capable of doing, the confirmed skeptic will insist on maintaining belief in his own irrational notions. This is due to either a great blindness, which renders him incapable of seeing what is plainly set before him, or on account of an opinionative obstinacy, which prevents him from acknowledging the truth of what he does see. Thence arises the woeful necessity of going to ridiculous lengths to expound yet more fully on what we have already made perfectly clear, in hopes that we might get through to those who close their minds to reason.
And yet how shall we ever profit from our discussions, or what bounds can be set to our discourse, if we forever fall to the temptation of replying to those who reply to us? We must acknowledge that those who are so hardened by the habit of contradiction will never yield, but would rather reply out of stubbornness, even when they recognize their own error.