Marx's Capital

I have the feeling that I've 'read' an entire book (in the sense of having read all the words in it) without it making any impression on me. It's hard to disentangle how much this reflects on the subject matter (I'm not sure any explanation of 'Capital' is going to be easy reading), how much is the writing style, how much is my, for want of a better phrase 'pandemic brain fog' (that's the "it's me, not you" side of book reviewing), and how much is the way I tend to glaze over when I see mathematical formulae in a text. Maybe I need to work up to books like this?