Why a wrong guess helps
Trying to answer questions about material you haven't studied yet — and mostly failing — makes the eventual explanation land harder. The wrong guess primes the question in your mind, so the correct answer has somewhere to attach.
Turn reading into a search
It reframes reading, too: instead of consuming pages, you're hunting for answers to questions you already care about, because you just got them wrong.
Try it before the chapter
Practically: before reading a new chapter or summary, quiz yourself cold on it first. Score doesn't matter; the attempt does.