Never Forget What You Read:
Science-Based Techniques Using Summaries & Review

"I loved that book, but a month later I can barely remember what it was about..."
"I read a lot, but I don't feel like the knowledge is sticking..."

Sound familiar? This is actually a universal experience. According to research by psychologist Hermann Ebbinghaus, humans forget approximately 70% of what they learn within 24 hours.

However, by using the "Summary × Review Method" to retain book content in your long-term memory, you can significantly prevent this "forgetting."

Why Do We Forget What We Read?

In other words, if you do nothing after reading, you'll forget roughly 80% of the book's content within a month. This is simply how the human brain works.

However, Reading Has an Advantage Over Nonsense Syllables

Ebbinghaus's experiments used meaningless syllables, but book content has context and connections to existing knowledge, so it seems to be easier to remember than nonsense syllables.

However, the fact remains that without review, you will eventually forget it.

* Modern research confirms that without review, more than half of memories are lost within a day.

Two Keys to Memory Retention

However, Ebbinghaus's research also observed that review makes relearning easier, and that spaced learning is more effective than massed practice. Later cognitive psychology research has also shown that outputting learned content in your own words is effective for memory retention. Based on these findings, the keys to retention are "Output (Summarizing)" and "Spaced Repetition."

1. The Power of Output (Summarizing)

Summarizing what you've read in your own words helps transfer information from "short-term memory" to "long-term memory." This is called "elaborative rehearsal," and it's more effective than simply re-reading.

2. The Power of Spaced Repetition (Spacing Effect)

Research shows that reviewing multiple times with intervals between is more effective than studying for extended periods at once. This is known as the "spacing effect" or "distributed practice." Ebbinghaus himself discovered this effect, and it has been widely confirmed in modern cognitive science.

The optimal timing for review is "just before you forget." Too late and you've already forgotten; too early and the memory is still too fresh for the review to be effective. Reviewing at the point where you can "just barely recall" maximizes memory consolidation efficiency.

Latest Neuroscience Validates These Methods (2024-2025 Research)

140 years after Ebbinghaus's research, modern neuroscience and cognitive science have not only validated his discoveries but also revealed even more effective learning strategies.

The Testing Effect: Scientific Validation

Rather than immediately re-reading your summary during review, "trying to recall what was written first" is more effective for memory retention—this phenomenon, known as the Testing Effect (or Retrieval Practice), has been the subject of 1,215 peer-reviewed papers published between 1999 and 2022. Meta-analyses confirm a medium effect size (g=0.50), and the effect has been proven effective even for complex content like medicine and physiology.

In other words, when reviewing, the most effective approach is: "First try to recall the content without looking at your notes → Then check and supplement with your notes." Having summaries allows you to verify whether what you recalled was correct, improving memory accuracy.

Interleaved Replay During Sleep

Research from 2024-2025 has revealed remarkable findings about memory processing during sleep. During deep non-REM sleep, the brain alternates between replaying new and existing memories—a newly discovered phenomenon. This "interleaved replay" prevents "catastrophic forgetting"—where new learning overwrites old memories—and systematically integrates knowledge into long-term storage.

Interleaving Learning

Research shows that alternating between related but different topics improves flexibility and application skills. For example, reading books from different genres alternately rather than consecutively makes each easier to distinguish and more likely to be retained in long-term memory.

Practice: The Summary × Review Method

So how do you put this into practice? Follow these 3 steps to dramatically improve your reading retention:

1. Write Summaries As You Read (Chapter/Section by Section)
   Important: Waiting until you finish the book is too late. If it takes days or weeks to read a book, you'll have forgotten much of what you read by the time you finish.
   • Textbooks, technical books, challenging works: Record by section (ideal)
   • Business books, non-fiction: Record by chapter (practical)
   • Novels, essays: Recording after finishing is OK (narrative flow matters)
   After each chapter or section, briefly note in your own words "What was the key point?" and "What stood out to me?" Rather than copying text verbatim, rephrasing in your own words dramatically improves retention.
2. Save Meaningful Quotes Immediately
   When you find a phrase that resonates or an important sentence, record it right then. If you think "I'll write it down later," you'll forget which page it was on. Adding a brief note about why it struck you will help the original understanding resurface when you review later.
3. Build a Habit of Regular Recall & Review
   Set regular times—weekends or the start of each month—to revisit past readings. The key is to first try to recall "what was that book about?" without looking at your notes. This "active recall" is what strengthens memory. After recalling, check your notes to fill in any gaps you missed. With chapter-by-chapter notes recorded as you read, this verification takes just minutes.

Practice with Reading Forest

"Reading Forest" is a reading record tool designed specifically to implement this "Summary × Review Method."

Works on both smartphone and computer, so you can quickly jot down thoughts about a book you read on the train, or spend your weekend reviewing past records on your computer.

Summary

Forgetting what you read isn't a matter of memory ability. It's an unavoidable phenomenon due to how the human brain works.

However, using the scientifically proven "Summary × Review Method," you can retain knowledge from reading as long-term memory.

Start today and transform your reading from "read and forget" to "read and remember."

References & Sources