It is hugely effective to have multiple physical books around you on the same subject at different levels of detail and different explanation approaches.
It makes it very easy to switch books in midstream if you get stuck, gain more understanding from another book, and then come back to the original book with renewed insight.
Getting stuck... that's a killer. Now, if I've decided to learn something, I get at least 2 books on the same topic. If one author's explanation doesn't click for me, it's good to have that second book for a different explanation.
It makes it very easy to switch books in midstream if you get stuck, gain more understanding from another book, and then come back to the original book with renewed insight.