WIST

If we could learn to look, instead of gawking,
We’d see the horror in the heart of farce.
If only we could act, instead of talking,
We wouldn’t always end up on our arse.
This is the thing that nearly had us mastered;
Don’t yet rejoice in his defeat, you men!
Although the world has stood up and stopped the bastard,
The bitch that bore him is in heat again.

[Ihr aber lernet, wie man sieht statt stiert
Und handelt, statt zu reden noch und noch.
So was hätt einmal fast die Welt regiert!
Die Völker wurden seiner Herr, jedoch
Dass keiner uns zu früh da triumphiert —
Der Schoß ist fruchtbar noch, aus dem das kroch.]

Bertolt Brecht (1898-1956) German poet, playwright, director, dramaturgist
The Resistible Rise of Arturo Ui [Der Aufhaltsame Aufstieg des Arturo Ui], Epilogue (1941) [tr. Tabori (1963)]
    (Source)

Original German. The end of the play, after the violent death of the gangster Ui, modeled after the rise of Hitler. It was not performed until 1958 (German), 1960 (English). The above is the translation first used on Broadway (1963).

The last three lines are in the credits of the Sam Peckinpah (dir.) film Cross of Iron (1977).

Alternate translations:

Therefore we learn how to see and not to gape.
To act instead of talking all day long.
The world was almost won by such an ape!
The nations put him where his kind belong.
But don't rejoice too soon at your escape --
The womb he crawled from is still going strong.
[tr. Manheim (1981)]

The last four lines of Manheim's version were quoted by a vampire in the final episode of the first series (UK) of Being Human (2008).

Learn how to face the facts you tried to shun.
And how to act, where once you idly slept.
That's how the world was going to be run!
The nations duly mastered it, except
(In case you think the battle has been won) --
The womb is fertile still from which that crept.
[tr. Willett]

That was similar to the quatrain Willett translated (1998) from the portion of that that Brecht used in his War Primer [Kriegsfibel] (1947):

That’s how the world was going to be run!
The other nations mastered him, except
(In case you think the battle has been won) --
The womb is fertile still from which that crept.

Something like that almost governed the world.
Yet the people mastered him. But
I wish you'd hold your triumph:
The womb is fertile still from which that crawled.
[Another Kriegsfibel trans.]

Let none of us exult too soon: the womb is fertile still from which this monster crawled.
[Notes from Brecht in the notes for José Limón's unfinished memoir]

Do not applaud quite so soon, for the womb is fertile still from where this one crawled.
[Source]