A friend recently recommended a book by an author whose previous book I had read. She asked me, “What was that (prior) book about?” My response: “Uh. . . umm . . . I can’t remember.” I had drawn a total blank — I couldn’t recall the main characters or even the plot. The only thing I could remember was a vague recollection that I had liked it.

I bet this happens to you, too — you don’t remember the details of many of the books you read, movies you watch, or most other experiences. And then there are all the mundane things like your morning commute, what you had for lunch two weeks ago, and details of conversations with other people that we don’t remember at all.  We tend to remember recent events (I ate at Frida’s yesterday, and I was in Florida last week), but as time passes, most of our memories fade. And we tend to only remember the peaks and ends of experiences (this is called the peak-end rule and you can read more about that here).

Our brains aren’t structured to remember most things — there’s an issue of capacity and processing power. Plus, if we remembered everything, it would likely drive us crazy (some people sort of can, and it is a blessing and curse). So, not remembering most things is normal.

The Ebbinghaus Forgetting Curve

A rule of thumb for how much we remember over time can be represented by the nearly 140-year-old “Ebbinghaus’ Forgetting Curve,” which was developed by German psychologist Hermann Ebbinghaus in the 1880s based on experiments he ran on himself. Research over the past 130+ years has generally confirmed Ebbinghaus’s results (see, e.g., this 2015 study)

The drop-off of what we remember is steep — we forget over half of our experiences within an hour!

How To Put Things Into Long-Term Memory

In one sense, there’s nothing we can do about the forgetting curve—our brains aren’t structured to remember everything. And that’s mostly fine — we don’t need to remember the mundane details of our minute-to-minute existence. But what do we do about things that we want to remember? Like things we want to learn?

Research has found that the key to putting things that we learn into long-term memory is structured repetition, which involves re-learning in different ways at spaced intervals. Here’s a helpful graphic representation:

Structured repetition works best when it is (1) spaced out (just repeating something over and over right away isn’t as effective) and (2) when how you learn it changes.

For example, if you are a student and want to learn something from a chapter of a textbook, you might:

• Read the chapter and highlight important sections
• Wait a few hours or days and then type out the important points
• A day or two later, make flashcards
• Then quiz yourself with the flashcards

I use spaced repetition on non-fiction books I want to remember. I highlight and take notes as I read. After I finish the book, I wait a few days and go back and read through my highlights. Sometimes, I read through them again days later. And more recently, I’ve been using AI like ChatGPT or Claude.ai to produce summaries of the important points of the book and read through these summaries (but I’ve also found that AI hallucinates 10-20% of the time and produces summaries that are totally incorrect). I find that this works pretty well.