I think mankind's existence could be synopsized in a brief metaphor:

A ship represents man, and the world represents the universe.

Man is currently on a journey, threshing through the waters of this planet. The planet presents an infinite course, seeing as it is a spheroid. So man charts this course using his own measurement tools, trying to calibrate the proper direction. However, because these tools never succinctly coincide with what the course should be, he must constantly recheck and remeasure. This, in effect, becomes a perennial cycle. However, the cycle collapses if the world is flat (meaning, it has a beginning and an end), or if our ship is dashed upon some rock somewhere in an unfortunate turn of events.