Full Idea
As the subject of willing I am an exceedingly wretched being, and all our suffering consistd in willing, ...but as soon as I am absorbed in knowledge, I am blissfully happy and nothing can assail me.
Gist of Idea
As the subject of willing I am wretched, but absorption in knowledge is bliss
Source
Arthur Schopenhauer (Manuscript remains [1855], I p.137), quoted by Peter B. Lewis - Schopenhauer 4
Book Reference
Lewis, Peter B.: 'Schopenhauer' [Reaktion Books 2012], p.90
A Reaction
So the source of his pessimism is subjection to his own will. However, since becoming absorbed in knowledge is an easy task for a scholar, he has little to grumble about. Nietzsche mocked the great pessimist for playing the flute every day.