"Be kinder than necessary because everyone you meet is fighting some kind of battle."
Philo of Alexandria (20 BC - 50 AD)
Philo of Alexandria, also called Philo Judaeus, was a Hellenistic Jewish philosopher who lived in Alexandria, in the Roman province of Egypt. Philo used philosophical allegory to attempt to fuse and harmonize Greek philosophy with Jewish philosophy. Wikipedia
To learn more http://en.wikipedia.org/wiki/Philo
Source of this quote http://wiki.answers.com/Q/Who_said_Be_kinder_than_necessary_because_everyone_you_meet_is_fighting_some_kind_of_battle
Thank you to my friend Mary Ellen for sharing a similar quotation attributed to Plato.