“Attributed to Plato in No Ordinary Moments: A Peaceful Warrior's Guide to Daily Life (1992) by Dan Millman. It has also been wrongly attributed to Philo. It is a variant of the Christmas message "Be pitiful, for every man is fighting a hard battle," written by the Scottish preacher Ian Maclaren (also known as John Watson) in 1897.”
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Source: Wikiquote