Oh--just that I couldn't understand the first chapter in Stepanov fully on first reading, so I need to read it again (and again, and again).
The Feynman reference is
Well, I asked him, “How can I read it?
It’s so hard.” He said, “You start at the
beginning and you read as far as you can
get, until you are lost. Then you start at
the beginning again, and you keep working
through until you can understand the whole
book.”
—Joan Feynman, Richard Feynman’s sister,
recalling a discussion with her brother
The Feynman reference is
From https://rs.io/feynman-reading-difficult-things/