Yes perhaps, as the Sage says, "nothing worthy of proving can be proven, nor yet disproven"; but can we restrain that instinct which urges man to wish to know, and above all to wish to know the things which conduce to life, to eternal life? Eternal life, not eternal knowledge as the Alexandrian gnostic said. For living is one thing and knowing is another; and... perhaps there is an opposition between the two that we may say that everything vital is anti-rational, not merely irrational, and that everything rational is anti-vital. And this is the basis of the tragic sense of life.

The Tragic Sense of Life (1913) - II : The Starting-Point