I came across this just now and thought I’d post it. In a letter to his mother from 1918, Franz Rosenzweig—while reading through Hermann Cohen’s Logic of Pure Cognition—writes
Cohen is insanely hard. I would never have believed that a philosophical book would hold such difficulties for me. Moreover-whether understanding him is accordingly worthy, is not yet certain for me; I almost believe it is not. But now I have begun it and am reading it through.
Rosenzweig, of course, ends up taking up Cohen’s infinitesimal method (of sorts) in the Star, but I find this passage somewhat comforting.