“I suppose [...] that the most convincing way to fool an enemy would be to fool a friend.”
“My enemies are everywhere, and my friends are fools.”
“Every fool stands convinced; and everyone convinced is a fool. The faultier a person's judgement the firmer their convictions.”
“I am for the most part so convinced that everything is lacking in basis, consequence, justification, that if someone dared to contradict me, even the man I most admire, he would seem to me a charlatan or a fool.”
“It's easier to fool people than to convince them that they have been fooled.”
“A wise man gets more use from his enemies than a fool from his friends.”