As Durer knew full well, there is a center and final substance in mathematics whose perfect beauty is rational, but rational "in retrospect." The discovery which comes before, those rare moments which elevate man, and the searchings of the heart which come after are not rational. They are groupings filled with wonder and sometimes sorrow.

In: Raymond George Ayoub, Musings of the Masters: An Anthology of Mathematical Reflections, Mathematics and the Arts (p. 92)