euthydemus   

True.
Well, Cleinias, but if you have the use as well as the possession of
good things, is that sufficient to confer happiness?
Yes, in my opinion.
And may a person use them either rightly or wrongly?
He must use them rightly.
That is quite true, I said. And the wrong use of a thing is far worse
than the non-use; for the one is an evil, and the other is neither a
good nor an evil. You admit that?
He assented.
Now in the working and use of wood, is not that which gives the right
use simply the knowledge of the carpenter?
Nothing else, he said.
And surely, in the manufacture of vessels, knowledge is that which
gives the right way of making them?
He agreed.
And in the use of the goods of which we spoke at first-wealth and
health and beauty, is not knowledge that which directs us to the right
use of them, and regulates our practice about them?
He assented.
Then in every possession and every use of a thing, knowledge is that
which gives a man not only good-fortune but success?
He again assented.
And tell me, I said, O tell me, what do possessions profit a man, if
he have neither good sense nor wisdom? Would a man be better off,
having and doing many things without wisdom, or a few things with
wisdom? Look at the matter thus: If he did fewer things would he not
make fewer mistakes? if he made fewer mistakes would he not have fewer
misfortunes? and if he had fewer misfortunes would he not be less
miserable?
Certainly, he said.
And who would do least-a Poor man or a rich man?
A poor man.
A weak man or a strong man?
A weak man.
A noble man or a mean man?
A mean man.
And a coward would do less than a courageous and temperate man?
Yes.
And an indolent man less than an active man?
He assented.
And a slow man less than a quick; and one who had dull perceptions of
seeing and hearing less than one who had keen ones?
All this was mutually allowed by us.
Then, I said, Cleinias, the sum of the matter appears to be that the
goods of which we spoke before are not to be regarded as goods in
themselves, but the degree of good and evil in them depends on whether
they are or are not under the guidance of knowledge: under the
guidance of ignorance, they are greater evils than their opposites,
inasmuch as they are more able to minister to the evil principle which
rules them; and when under the guidance of wisdom and prudence, they
are greater goods: but in themselves are nothing?
That, he replied, is obvious.
What then is the result of what has been said? Is not this the
result-that other things are indifferent, and that wisdom is the only
good, and ignorance the only evil?
He assented.
Let us consider a further point, I said: Seeing that all men desire
happiness, and happiness, as has been shown, is gained by a use, and a
right use, of the things of life, and the right use of them, and good
fortune in the use of them, is given by knowledge,-the inference is
that everybody ought by all means to try and make himself as wise as
he can?
Yes, he said.