"Whenever calamity howlers shake their heads and impress upon you that this, that, and the next dire catastrophe is to befall this nation or the nations of the world-such as, for example, that exhaustion of the world's oil supply will bring all transportation and machinery to a standstill through lack of lubrication, or that exhaustion of the earth's stores of coal will make life unlivable in these cold climates-just smile and reply that the worst troubles of all are those that never happen [and] that you prefer not to cross shaky bridges until you come to them."