"What does the entire history of socialism and of all modern revolutions show us? The first spark of class struggle in Europe, the revolt of the silk weavers in Lyon in 1831, ended with a heavy defeat; the Chartist movement in Britain ended in defeat; the uprising of the Parisian proletariat in the June days of 1848 ended with a crushing defeat; and the Paris commune ended with a terrible defeat. The whole road of socialism – so far as revolutionary struggles are concerned – is paved with nothing but thunderous defeats. Yet, at the same time, history marches inexorably, step by step, toward final victory! Where would we be today without those “defeats,” from which we draw historical experience, understanding, power and idealism? Today, as we advance into the final battle of the proletarian class war, we stand on the foundation of those very defeats; and we can do without any of them, because each one contributes to our strength and understanding.
[...]
“Order prevails in Berlin!” You foolish lackeys! Your “order” is built on sand. Tomorrow the revolution will “rise up again, clashing its weapons,” and to your horror it will proclaim with trumpets blazing: I was, I am, I shall be!"
http://www.marxists.org/archive/luxemburg/1919/01/14.htm