“Because the world owes me nothing
And we owe each other the world.”

Misattributed
Source: Often attributed to Twain, but sourced to Robert J. Burdette, Quote Investigator http://quoteinvestigator.com/2014/06/06/world-owes/

No tienes nada y me darías un mundo. Te debo un mundo.
Voces (1943)

Source: The Astral

De Re Militari (also Epitoma Rei Militaris), Book I, "The Selection and Training of New Levies"
Context: Victory in war does not depend entirely upon numbers or mere courage; only skill and discipline will insure it. We find that the Romans owed the conquest of the world to no other cause than continual military training, exact observance of discipline in their camps and unwearied cultivation of the other arts of war. Without these, what chance would the inconsiderable numbers of the Roman armies have had against the multitudes of the Gauls? Or with what success would their small size have been opposed to the prodigious stature of the Germans? The Spaniards surpassed us not only in numbers, but in physical strength. We were always inferior to the Africans in wealth and unequal to them in deception and stratagem. And the Greeks, indisputably, were far superior to us in skill in arts and all kinds of knowledge. (Book 1)

taken from 'Brandalism' in the book 'Cut It Out' (inspired from Sean Tejaratchi's piece in Crap Hound No.6, July 1999.) Source http://readingfrenzy.com/ledger/2012/03/taking_the_piss_conclusion
Other sources
Source: Wall and Piece
Context: People are taking the piss out of you every day. They butt into your life, take a cheap shot at you and then disappear. They leer at you from tall buildings and make you feel small. They make flippant comments from buses that imply you’re not sexy enough and that all the fun is happening somewhere else. They are on TV making your girlfriend feel inadequate. They have access to the most sophisticated technology the world has ever seen and they bully you with it. They are The Advertisers and they are laughing at you. You, however, are forbidden to touch them. Trademarks, intellectual property rights and copyright law mean advertisers can say what they like wherever they like with total impunity. Fuck that. Any advert in a public space that gives you no choice whether you see it or not is yours. It’s yours to take, re-arrange and re-use. You can do whatever you like with it. Asking for permission is like asking to keep a rock someone just threw at your head. You owe the companies nothing. Less than nothing, you especially don't owe them any courtesy. They owe you. They have re-arranged the world to put themselves in front of you. They never asked for your permission, don't even start asking for theirs.

I Believe

Source: Course of Experimental Philosophy, 1745, p. vi: Preface
Context: It is to Sir Isaac Newton's Application of Geometry to Philosophy, that we owe the routing of this Army of Goths and Vandals in the philosophical World; which he has enriched with more and greater Discoveries, than all the Philosophers that went before him: And has laid such Foundations for future Acquisitions, that even after his Death, his Works still promote natural Knowledge. Before Sir Isaac, we had but wild Guesses at the Cause of the Motion of the Comets and Planets round the Sun', but now he has clearly deduced them from the universal Laws of Attraction (the Existence of which he has proved beyond Contradiction) and has shewn, that the seeming Irregularities of the Moon, which Astronomers were unable to express in Numbers, are but the just Consequences of the Actions of the Sun and Earth upon it, according to their different Positions. His Principles clear up all Difficulties of the various Phænomena of the Tides; and the true Figure of the Earth is now plainly shewn to be a flatted Spheroid higher at the Equator than the Poles, notwithstanding many Assertions and Conjectures to the contrary.

Quoted in the New York World (11 May 1901) during the Northern Pacific Corner. See Morgan: American Financier by Jean Strouse

Si no nos dieran nada quienes no nos deben nada, !pobres de nosotros!
Voces (1943)