He's saying that if you learn of an argument that shows Fact A to be false, instead of Fact A being deleted from your brain, that argument will be stored as Fac

He's saying that if you learn of an argument that shows Fact A to be false, instead of Fact A being deleted from your brain, that argument will be stored as Fact B in your brain. If Fact B is not sufficiently well-integrated in to your thinking then you will pretty much continue to believe Fact A. BTW don't feel bad that you couldn't understand his sentence, it was pretty hackneyed.