Be kind, for everyone you meet is fighting a hard battle.

Original: “’Be pitiful, for every man is fighting a hard battle,’ was the tender Christmas message sent by Ian Maclaren to the readers of The British Weekly.”

The original, dating from 1898, uses an unfamiliar definition of “pitiful” and uses the gender-specific “man,” so the modernized version is understandably more popular. http://quoteinvestigator.com/2010/06/29/be-kind/ )

I’ve often seen this statement attributed to Plato.