"To be criticised is not always to be wrong."
-- Anthony Eden

"Any fool can criticise and most fools do."
-- Patrick Barlow (though it may have a prior origin)

"Answer not a fool according to his folly, lest thou also be like unto him."
-- Proverbs

"A fool can always find a greater fool to admire him."
-- Niolas Boilean

"A man of genius makes no mistakes. His errors are volitional and are the portals of discovery."
-- James Joyce

"He who discommendeth others obliquely commendeth himself."
-- Thomas Browne