The disease of pilgrims
They came because they were afraid or unafraid, because they were happy or unhappy, because they felt like Pilgrims or did not feel like Pilgrims. There was a reason for each man. They were leaving bad wives or bad jobs or bad towns; they were coming to find something or leave something or get something, to dig up something or bury something or leave something alone. But a government finger pointed from four-color posters in many towns: THERE'S WORK FOR YOU IN THE SKY: SEE MARS! and the men shuffled forward, only a few at first, a double-score, for most men felt the great illness in them even before the rocket fired into space. And this disease was called The Lonliness.
- Ray Bradbury, The Martian Chronicles.