“If fighting is sure to result in victory, then you must fight, even though the ruler forbid it; if fighting will not result in victory, then you must not fight even at the ruler's bidding.”
Source: The Art of War, Chapter X · Terrain
Original
故戰道必勝,主曰無戰,必戰可也;戰道不勝,主曰必戰,无戰可也;
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Sun Tzu 68
ancient Chinese military general, strategist and philosophe… -543–-495 BCRelated quotes

“We must fight our way to victory on a sea of blood and a horizon of fire.”
As quoted in the Wall Street Journal (14 November 1969)

“You can't live without illusions, even if you must fight for them.”

“Fight, and you shall win. For God grants victory to perseverance.”
As quoted in Simón Bolívar (1969) by Gerhard Masur
Context: Do not compare your material forces with those of the enemy. Spirit cannot be compared with matter. You are human beings, they are beasts. You are free, they are slaves. Fight, and you shall win. For God grants victory to perseverance.

Source: The Subtle Art of Not Giving a F*ck (2016), Chapter 2, “Happiness Is a Problem” (p. 40)
“What you cannot escape, you must fight; what you cannot fight, you must endure.”
Source: The Devil's Right Hand

“The North is fighting for no sentimental cause—for no victory of a 'higher civilization.'”
It is fighting for a very ancient and vulgar object of war—for that which Russia has secured in Poland—that which Austria clings to in Venetia—that which Napoleon sought in Spain. It is a struggle for empire, conducted with a recklessness of human life which may have been paralleled in practice, but has never been avowed with equal cynicism. If any shame is left in the Americans, the first revision they will make in their constitution will be to repudiate formally the now exploded doctrine laid down in the Declaration of Independence, that 'Governments derive their just powers from the consent of the governed'.
Source: 'The United States as an Example', Quarterly Review, 117, 1865, pp. 252-253