“Constantly at war, the tribesmen fought one another with pitiless ferocity, and only the very strong survived to manhood.”

Source: Drenai series, Legend, Pt 1: Against the Horde, Ch. 12
Context: There is only one way to survive in war, and that is by being willing to die. You will find soon that swordsmen can be downed by untutored savages who would slice their fingers if asked to carve meat. And why? because the savage is willing. Worse, he may be a baresark.

"The Vietnam Negotiations", Foreign Affairs, Vol. 48, No. 2 (January 1969), p. 214; also quoted as "A conventional army loses if it does not win. The guerilla army wins if he does not lose."
1960s
Context: We fought a military war; our opponents fought a political one. We sought physical attrition; our opponents aimed for our psychological exhaustion. In the process we lost sight of one of the cardinal maxims of guerrilla war: the guerrilla wins if he does not lose. The conventional army loses if it does not win. The North Vietnamese used their armed forces the way a bull-fighter uses his cape — to keep us lunging in areas of marginal political importance.

Source: The Crossing

How Dangerous Are Atomic Weapons?, 1947

Annals, Book V

Beast and Man: The Roots of Human Nature (1979). 168.
Context: Creatures really have divergent and conflicting desires. Their distinct motives are not (usually) wishes for survival or for means-to-survival, but for various particular things to be done and obtained while surviving. And these can always conflict. Motivation is fundamentally plural. It must be so because, in evolution, all sorts of contingincies and needs arise, calling for all sorts of different responses. An obsessive creature, constantly dominated by one kind of motive, would not survive.

Remarks in the Senate, February 2, 1954, Congressional Record, vol. 100, p. 1106.

Source: Drenai series, Legend, Pt 1: Against the Horde, Ch. 7

Address to the 75th annual convention of the Veterans of Foreign Wars, Chicago, Illinois (19 August 1974)
1970s