Aristotle

What lies in our power to do, it lies in our power not to do.

Happiness does not consist in pastimes and amusements but in virtuous activities

Suffering becomes beautiful when anyone bears great calamities with cheerfulness, not through insensibility but through greatness of mind.

All human actions have one or more of these seven causes: chance, nature, compulsion, habit, reason, passion, and desire.

In all things of Nature, there is something of the marvelous.

Humor is the only test of gravity, and gravity of humor; for a subject which will not bear raillery is suspicious, and a jest which will not bear serious examination is false wit.

What is the essence of life?  To serve others and do good.

Love is the cause of unity in all things.

One swallow does not make a summer, neither does one fine day; similarly one day or brief time of happiness does not make a person entirely happy.

Dignity consists not in possessing honors, but in the consciousness that we deserve them.