“Dangers await only those who do not react to life.”

1961, Address to ANPA
Context: Today no war has been declared — and however fierce the struggle may be, it may never be declared in the traditional fashion. Our way of life is under attack. Those who make themselves our enemy are advancing around the globe. The survival of our friends is in danger. And yet no war has been declared, no borders have been crossed by marching troops, no missiles have been fired.
If the press is awaiting a declaration of war before it imposes the self-discipline of combat conditions, then I can only say that no war ever posed a greater threat to our security. If you are awaiting a finding of "clear and present danger," then I can only say that the danger has never been more clear and its presence has never been more imminent.
It requires a change in outlook, a change in tactics, a change in missions — by the government, by the people, by every businessman or labor leader, and by every newspaper. For we are opposed around the world by a monolithic and ruthless conspiracy that relies primarily on covert means for expanding its sphere of influence — on infiltration instead of invasion, on subversion instead of elections, on intimidation instead of free choice, on guerrillas by night instead of armies by day. It is a system which has conscripted vast human and material resources into the building of a tightly knit, highly efficient machine that combines military, diplomatic, intelligence, economic, scientific and political operations. Its preparations are concealed, not published. Its mistakes are buried, not headlined. Its dissenters are silenced not praised. No expenditure is questioned, no rumor is printed, no secret is revealed. It conducts the Cold War, in short, with a war-time discipline no democracy would ever hope or wish to match.
Nevertheless, every democracy recognizes the necessary restraints of national security — and the question remains whether those restraints need to be more strictly observed if we are to oppose this kind of attack as well as outright invasion.

Source: Seize the Night

Source: By the Time You Read This, I'll Be Dead

Book I, Chapter 5, "We Have Cause to Be Uneasy"
Mere Christianity (1952)
Context: Some people talk as if meeting the gaze of absolute goodness would be fun. They need to think again. They are still only playing with religion. Goodness is either the great safety or the great danger—according to the way you react to it.

Source: What's the Worst That Could Happen?: A Rational Response to the Climate Change Debate (2009), Chapter 1 "The Decision Grid" (p. 19)

"Meeting Of The All-Russia Central Executive Committee" (4 November 1917) http://www.marxists.org/archive/lenin/works/1917/nov/04a.htm; Collected Works, Vol. 26, pp. 285-293.
1910s

Source: Codependent No More: How to Stop Controlling Others and Start Caring for Yourself

"All for the Good: Why genetic engineering must soldier on" in TIME magazine, Vol. 153, No. 1 (11 January 1999) http://www.mindfully.org/GE/Soldier-On-James-Watson.htm
Context: When anti-DNA doomsday scenarios failed to materialize, even the modestly restrictive governmental regulations began to wither away. In retrospect, recombinant-DNA may rank as the safest revolutionary technology ever developed. To my knowledge, not one fatality, much less illness, has been caused by a genetically manipulated organism.
The moral I draw from this painful episode is this: Never postpone experiments that have clearly defined future benefits for fear of dangers that can't be quantified. Though it may sound at first uncaring, we can react rationally only to real (as opposed to hypothetical) risks.