The universe is probably littered with the one-planet graves of cultures which made the sensible economic decision that there's no good reason to go into space--each discovered, studied, and remembered by the ones who made the irrational decision. - Randall Munroe From XKCD 893, 65 years, with a chart demonstrating that in a fairly short period of time the number of living humans who have ever stepped on another world will reach zero very soon. https://xkcd.com/893/
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