The expert is usually a man who has stopped thinking and so is perfectly able to be utterly wrong for at least the rest of his lifetime. He has made up his mind, not upon principle, but upon expedient practice.
[Source, Frank Lloyd Wright: An Autobiography, Book 5 "Form" (1943)]

An expert? Generally a man who has stopped thinking because he knows!
[Source]

An expert is a man who has stopped thinking -- he knows.
[Source, in Earl Nesbit, Taliesin Reflections (2006)]

To me an expert is a man who has stopped thinking. He thinks he knows everything.
[Source, in Patrick J. Meehan, Truth Against the World (1987)]

Now, an "expert" is a man who has stopped thinking. He has had to stop thinking or he would be no expert. You can't call a man an "authority" who is growing and so changing his mind about things, can you? No, the expert has got to know or profess he knows. He's got to stand there and be knowledgeable! Well, too bad, because there's no such human except he be somewhat a phoney.
[Source, in Patrick J. Meehan, Truth Against the World (1987)]

An expert is a man who has stopped thinking because he knows and you can do nothing with him if you got a good idea.
[Source, in Patrick J. Meehan, The Master Architect (1984)

But that a man, how wise soe'er, should learn
In many things and slack his stubborn will,
This is no derogation. When the streams
Are swollen by mountain-torrents, thou hast seen
That all the trees wich bend them to the flood
Preserve their branches from the angry current,
While those which stem it perish root and branch.
[tr. Donaldson (1848)]

The wisest man will let himself be swayed
By others' wisdom and relax in time.
See how the trees beside a stream in flood
Save, if they yield to force, each spray unharmed,
But by resisting perish root and branch.
[tr. Campbell (1873)]

'Tis no disgrace even to the wise to learn
And lend an ear to reason. You may see
The plant that yields where torrent waters flow
Saves every little twig, when the stout tree
Is torn away and dies.
[tr. Storr (1859)]

No, even when a man is wise, it brings him no shame to learn many things, and not to be too rigid. You see how the trees that stand beside the torrential streams created by a winter storm yield to it and save their branches, while the stiff and rigid perish root and all?
[tr. Jebb (1891)]

True wisdom will be ever glad to learn,
And not too fond of power. Observe the trees,
That bend to wintry torrents, how their boughs
Unhurt remain; while those that brave the storm,
Uprooted torn, shall wither and decay.
[tr. Werner (1892)]

No, though a man be wise, 'tis no shame for him to learn many things, and to bend in season. Seest thou, beside the wintry torrent's course, how the trees that yield to it save every twig, while the stiff-necked perish root and branch?
[tr. Jebb (1917)]

It is not reason never to yield to reason!
In flood time you can see how some trees bend,
And because they bend, even their twigs are safe,
While stubborn trees are torn up, roots and all
[tr. Fitts/Fitzgerald (1939), l. 570ff]

It is no weakness for the wisest man
To learn when he is wrong, know when to yield.
So, on the margin of a flooded river
Trees bending to the torrent live unbroken,
While those that strain against it are snapped off.
[tr. Watling (1947), l. 608ff]

A man, though wise, should never be ashamed
of learning more, and must unbend his mind.
Have you not seen the trees beside the torrent,
the ones that bend them saving every leaf,
while the resistant perish root and branch?
[tr. Wyckoff (1954)]

There's no disgrace, even if one is wise,
In learning more, and knowing when to yield.
See how the trees that grow beside a torrent
Preserve their branches, if they bend; the others,
Those that resist, are torn out, root and branch.
[tr. Kitto (1962)]

But a wise man can learn a lot and never be ashamed;
He knows he does not have to be rigid and close-hauled.
You've seen trees tossed by a torrent in a flash flood:
If they bend, they're saved, and every twig survives,
But if they stiffen up, they're washed out from the roots.
[tr. Woodruff (2001)]

But for a man, even if he is wise, to go on learning
many things and not to be drawn too taut is no shame.
You see how along streams swollen from winter floods
some trees yield and save their twigs,
but others resist and perish, root and branch.
[tr. Tyrell/Bennett (2002)]

On the contrary, it is no shame for even a wise man to continue learning. Nor should a man be obstinate. One can see the trees on the heavy river-banks. Those that bend with the rushing current, survive, whereas those bent against it are torn, roots and all.
[tr. Theodoridis (2004)]

For any man,
even if he’s wise, there’s nothing shameful
in learning many things, staying flexible.
You notice how in winter floods the trees
which bend before the storm preserve their twigs.
The ones who stand against it are destroyed,
root and branch.
[tr. Johnston (2005), l. 804ff]

No, it's no disgrace for a man, even a wise man, to learn many things and not to be too rigid. You see how, in the winter storms, the trees yield that save even their twigs, but those who oppose it are destroyed root and branch.
[tr. Thomas (2005)]