"Be kind, for everyone you meet is fighting a hard battle." This saying is widely attributed on the internet to Plato. However, students of Plato will agree that this saying, even in translation, does not quite sound like it was written over 2,000 years ago.
Thanks to Quote Investigator, the quote's origin has been shown to be of more recent origin. John Watson, D.D. (1850-1907), a minister in the Free Church of Scotland (also serving as the 1896 Lyman Beecher lecturer at Yale University, and the moderator of the 1900 synod of the English Presbyterian Church) who wrote many successful books under the pseudonym of 'Ian Maclaren,' making him one of the most popular authors of his day in Great Britain and America, said in 1897/1898: "Be pitiful, for every man is fighting a hard battle."