Isocrates Quote

Consider that nothing in human life is stable; for then you will not exult overmuch in prosperity, nor grieve overmuch in adversity. Rejoice over the good things which come to you, but grieve in moderation over the evils which befall you, and in either case do not expose your heart to others; for it were strange to hide away one's treasure in the house, and yet walk about laying bare one's feelings to the world.

Verse 42. - To Demonicus