Convert each heading into a question, then answer it from memory before you read the section — and check afterward.

Instead of reading passively:

• Take a heading ("Symmetric encryption") and make it a question ("What is symmetric encryption, and what's its main weakness?").
• Attempt the answer from memory first.
• Read the section to confirm or correct.

The upfront guess primes you to notice what you didn't know (this also relates to the "desirable difficulty" of pre-testing). It costs a little friction, which is exactly why it works — effort during study is the price of retention.

The tables flipped: the retrieval group recalled 61% versus 40% for the re-study group.

One week after studying, the group that had tested themselves decisively beat the group that had re-read: 61% vs 40%.

The lesson isn't subtle: re-study wins in the next five minutes; retrieval wins when it counts, at a delay. Because real exams and real life happen after a delay, "testing beats restudy at a delay" is the single most important finding in this whole field — and the reason spacing your self-tests out (see the next mission) matters so much.