You should not surrender to these men once for all the rudders of your mind, as if of a ship, and follow them whithersoever they lead; rather, accepting from them only that which is useful, you should know that which ought to be overlooked. What, therefore, these things are, and how we shall distinguish between them, is the lesson which I shall teach you.

"these men" refers to teachers and "the famous men of the ancients," p. 381 - On Greek Literature