„[Wittgenstein was]… one of the most exciting intellectual adventures [of my life]. … [He had] fire and penetration and intellectual purity to a quite extraordinary degree. … [He] soon knew all that I had to teach. His disposition is that of an artist, intuitive and moody. He says[,] every morning he begins his work with hope, and every evening he ends in despair.“
(https://de.wikipedia.org/wiki/Ludwig_Wittgenstein#Leben_und_Werk)