Men of fair minds, and not given up to the overweening of self-flattery, are frequently guilty of it
 John Locke, An Essay Concerning Human Understanding (1689). copy citation

Context

“though he be guilty of much greater unreasonableness in his own tenets and conduct, which he never perceives, and will very hardly, if at all, be convinced of. 2. Not wholly from Self-love. This proceeds not wholly from self-love, though that has often a great hand in it. Men of fair minds, and not given up to the overweening of self-flattery, are frequently guilty of it; and in many cases one with amazement hears the arguings, and is astonished at the obstinacy of a worthy man, who yields not to the evidence of reason, though laid before him as clear as daylight. 3.” source