It has been said that aliens exist only within man's creative imagination, which had been ported to television shows, or even quite simply to a good source, as well as theme for entertainment.
This is precisely what had been believed, up until contact had actually been made. It was simply an ordinary day, walking with his bulldog in the park, when it is that all of a sudden, there had been a big part of the morning sky which turned to a dull color, in gray.
The daylight had soon disappeared, and this had occurred just as it was that the observer had decided to look up.
Link: They Made a Contact (aliens)