No rational argument will have a rational effect on a man who does not want to adopt a rational attitude.

The Open Society and Its Enemies (Princeton University Press, 2013 [originally published in two volumes in 1945]), Ch. 24, p. 436, Oracular Philosophy and the Revolt against Reason:
"We have to conclude from this that no rational argument will have a rational effect on a man who does not want to adopt a rational attitude. Thus a comprehensive rationalism is untenable."