Why can reviewing an idea twice, with a break in between, leave you remembering it better a week later than one long session?

Answer: The gap lets the memory go a bit cold, so the second review has to rebuild it.

The gap lets the memory go a bit cold, so the second review has to rebuild it. ✓ — Successfully recalling an idea after a gap can make it easier to retrieve later. When the earlier encounter is no longer fresh, bringing it back requires more effort than repeating it immediately. This is one explanation for the spacing effect; if you have forgotten so much that recall fails, a longer gap need not help.

Two sessions simply add up to more total study time, and more time on a topic means more learning. — More study time is not what defines the benefit of spaced review. Spaced and back-to-back sessions can use the same total minutes yet produce different long-term recall. The timing of the encounters matters, not just how long you spend.

The break clears away tiredness, so the second review gets sharper attention. — Reduced fatigue alone does not explain why spaced review improves later recall. A break can help you feel fresher, but it also makes the previous encounter less immediately accessible. Successfully bringing the idea back can strengthen your ability to retrieve it later.