As to the xkcd - It presumes that not only is the Mars rover human, but that it has the same wants and needs as we do. Also, that it wants to come home, but can't. It works because loneliness is universal and there's very few places lonelier than Mars. It's a lie, though. Consider the mars rover as a creature. It was born to go to mars, bred to go to mars, trained to go to mars, and the hopes and dreams of millions bouyed it on its way to mars. Through fire and drama it lands on mars and makes astonishing discovery after astonishing discovery. It continues its discoveries and its journeys through one lifetime, two, three. Ten. Twenty. Opportunity is the Methuselah of Mars, continuing to send back insight and wonder through forty lifetimes. That fucker ain't sad, he exultant.