Appears in large friendly letters on the cover of the HitchhikersGuideToTheGalaxy, which is perhaps why it has sold so well.

Good advice in most situations.

ThereIsNoSituationSoBadThatYouCantMakeItWorseByPanicking.

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Take an AmigaComputer, activate its narrator device, and execute this algorithm:

 volume = 10
 pitch = 440
 speed = 2

 for n from 1 to 100
	volume += 1
	pitch += 10
	speed *= 0.99
	speak (volume, pitch, speed, "Don't Panic!")
	sleep (speed)

The effect sounds absolutely terrifying...

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Also a catch phrase of 'Mr Jones the Butcher' from a British cult comedy TV series from the 1970's/80's called "Dad's Army" see - http://www.mgnet.karoo.net/dads%20army.htm Corporal Jones