Isocrates

Regard as your most faithful friends, not those who praise everything you say or do, but those who criticize your mistakes.

But I marvel when I observe these men setting themselves up as instructors of youth who cannot see that they are applying the analogy of an art with hard and fast rules to a creative process

Spend your leisure time in cultivating an ear attentive to discourse, for in this way you will find that you learn with ease what others have found out with difficulty.

And let no one suppose that I claim that just living can be taught for, in a word, I hold that there does not exist an art of the kind which can implant sobriety and justice into depraved natures. Nevertheless, I do think that the study of political discourse can help more than any other thing to stimulate and form such qualities of character

It is more important to know where you are going than to get there quickly. Do not mistake activity for achievement. Remember that there is nothing stable in human affairs, therefore avoid undue elation in prosperity or undue depression in adversity.

Of all our possessions, wisdom alone is immortal.

Abhor flatterers as you would deceivers; for both, if trusted, injure those who trust them. If you admit as friends men who seek your favor for the lowest ends, your life will be lacking in friends who will risk your displeasure for the highest good.

So far has Athens left the rest of mankind behind in thought and expression that her pupils have become the teachers of the world, and she has made the name of Hellas distinctive no longer of race but of intellect, and the title of Hellene a badge of education rather than of common descent.

Make no man your friend before inquiring how he has used his former friends; for you must expect him to treat you as he has treated them. Be slow to give your friendship, but when you have given it, strive to make it lasting; for it is as reprehensible to make many changes in one's associates as to have no friends at all. Neither test your friends to your own injury nor be willing to forego a test of your companions.

Conduct yourself towards your parents as you would have your children conduct themselves towards you.