Four, actually:

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

Plato (attributions vary)

There is nothing either good or bad, but thinking makes it so.

William Shakespeare (in HamLet)

Contentment comes not so much from great wealth as from few wants.

Epictetus

If you reject the food, ignore the customs, fear the religion, and avoid the people, you might better stay home.

James a. Michener