• Perhaps, in retrospect, there would be little motivation even for malevolent extraterrestrials to attack the Earth; perhaps, after a preliminary survey, they might decide it is more expedient just to be patient for a little while and wait for us to self-destruct.

    Carl Sagan (2011). “Billions & Billions: Thoughts on Life and Death at the Brink of the Millennium”, p.169, Ballantine Books