[helterskelter]

> I also tend to read multiple books at the same time. Sometimes it happens that I get so into a book that I put the rest on pause because the story is grabbing all my attention, but in general I like to have a few books that I read in parallel. Having only a single option can become boring. I generally mix fiction and non-fiction to have a broader choice.

This is actually one of the best ways to reinforce knowledge, if that's what you're reading for. Especially if you are reading about different, but related, topics. The idea is that you do a little bit of forgetting between reading sessions of a book and then have to force some recall of where you were at when you pick up the book a few days later, which reinforces the memory of what you've read.

WRT reading multiple books on different but related topics, you're giving yourself more material to build a working mental model of something, so if you're trying to teach yourself calculus, you'll probably learn it much better when you're reading it along with, say, a book on the history of rocketry, and/or a book on astronomy. The topics reinforce and integrate nicely with one another because of the big overlap with the mental models used -- learning something in rocketry or astronomy gives you a place to tie in something you learn from calculus, for instance. They're also different enough to give your mind a break so you have to practice some recall of what you've already gone over when you pick up your calculus book again.

Also from personal experience, rotating through a few books helps to keep you reading constantly. When I used to focus on a single book I'd put off reading if I was in an especially dry spot. Being able to pick up another book allows me to avoid the dry section for a while, while also preventing me from doing something less worthwhile like look at my phone.