“In all human affairs, and especially in those that relate to war, …leave always some room to fortune, and to accidents which cannot be foreseen.”
The General History, Book II, Ch. 4 (trans. by Hampton)
The Histories
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Polybius 15
ancient Greek historian -208–-126 BCRelated quotes

“Fortune leaves always some door open to come at a remedy.”
Don Quixote de la Mancha (1605–1615), Unplaced as yet by chapter
“The fashions of human affairs are brief and changeable, and fortune never remains long indulgent.”
Breves et mutabiles vices rerum sunt, et fortuna nunquam simpliciter indulget.
IV, 14, 20.
Historiarum Alexandri Magni Macedonis Libri Qui Supersunt, Book IV

Pat Sajak, "Searching for the Next GOP Villain," in Human Events, 04/15/05 ( online http://freerepublic.com/focus/f-news/1384786/posts at freerepublic.com)
2000s

“Fortune, which has a great deal of power in other matters but especially in war, can bring about great changes in a situation through very slight forces.”
Sed fortuna, quae plurimum potest cum in reliquis rebus tum praecipue in bello, parvis momentis magnas rerum commutationes efficit; ut tum accidit.
The Civil War, Book III, 68; variant translation: "In war, events of importance are the result of trivial causes."

Press conference, New Delhi (October 19, 1971), quoted in "Indian and Pakistani Armies Confront Each Other Along Borders" by Sydney H. Schanberg, The New York Times (October 20, 1971), page 6C.

“There is no accident in our choice of reading. All our sources are related.”

“War isn’t declared in the name of God; it is a human affair entirely.”

http://books.google.com/books?id=FnAEAAAAYAAJ&q=%22I+own+it+is+a+common+saying+that+every+reverse+of+fortune+teaches+us+how+to+behave+on+another+occasion+but+that+is+not+true+as+the+circumstances+which+attend+each+event+are+different+and+such+as+could+not+be+foreseen%22&pg=PA321#v=onepage
Gli è ben vero che si dice Tu imparerai per un'altra volta: questo non vale perchè la vien sempre con modi diversi e non mai immaginati.
http://books.google.com/books?id=AIEOAAAAQAAJ&q=%22Gli+%C3%A8+ben+vero+che+si+dice+Tu+imparerai+per+un'altra+volta+questo+non+vale+perch%C3%A8+la+vien+sempre+con+modi+diversi+e+non+mai+immaginati%22&pg=PA181#v=onepage
Autobiography, vol. 2, ch. 9