The creator of the universe loves circles:

time and space are circles, the day is a circle, the year is a circle, the earth is a circle.

But when creating and fashioning the human heart, the creator only created a half-circle, so that there is something ontologically unfinished in human nature.

John O’Donohue

In the torment of the insufficiency of everything attainable,

we finally learn that here in this life all symphonies must remain unfinished.

Karl Rahner, sj., Catholic theologian