Conscience is the inner voice that warns us that someone might be looking. H. L. Mencken
History warns us that it is the customary fate of new truths to begin as heresies and to end as superstitions. Thomas Henry Huxley
The proverb warns that 'You should not bite the hand that feeds you.' But maybe you should, if it prevents you from feeding yourself. Thomas Szasz
Who threatens, warns. German Proverb
An overturned cart ahead warns the one behind. Chinese Proverb
A friend is one who warns you. Traditional Proverb