Created: May 5, 2026 Last Modified: May 5, 2026
This piece is a submission for IndieWeb Carnival May 2026: Write a love letter.
For a long time, flashcards were not on my radar for effective learning. I used it for English vocabulary when I was learning English as a teen, but I never considered using it for subjects that require deep understanding. When thinking about flashcards, an image that swiftly sprang to mind was of someone who mechanically memorizes definitions and equations, brute-forces through exams without comprehension. Such rote memorization is indeed detrimental to learning. This sentiment is common in STEM fields. A quick search leads to reddit posts like this where higher upvoted answers dismiss the value of flashcards.
My perception changed through the learning how to learn course, where I relearned about Spaced repetition, the technique of reviewing topics at increasing intervals. Using spaced repetition as a general-purpose learning tool (rather than just for rote memorization of vocabulary) was perhaps the most important thing I learned from that course. The course also specifically mentioned Anki, perhaps the most famous flashcard software, as a way to facilitate spaced repetition.
I had a particular reason to take this seriously: my memory is terrible. I often even forget what I did the day before, and the same goes for things I’ve studied. Math is the worst. I learned it in intensive bursts, but I rarely use it day to day, and what I study now might not be useful for another five years. Naturally, calculus, linear algebra, probability, and even high school trigonometry have all quietly slipped away.
It turns out that math is very cumulative: theorems built upon theorems. If I am not fluent in the basics, I will quickly be inundated with all the new material. There is a psychological concept called chunking that describes the inverse of this: once one internalizes the basics, they can think at a higher level of abstraction. From this perspective, fields that require deep understanding, like math, require memory just as fields with a breadth of shallow knowledge do, though in different ways.
Now you may think that with today’s abundance of information, we can look up everything pretty quickly. That is true. But the quickest search is slower than your brain. Moreover, not everything can be easily looked up, especially what falls into insights rather than definitions. When you look it up, you will only find lengthy articles to impart their wisdom, and that will take weeks to digest (again, if you have learned but forgotten).
How do I actually use flashcards? My software of choice is Anki. I am not completely satisfied with it. The UI looks dated, the WYSIWYG HTML editor is clunky, and the undocumented file format makes potential porting and interoperability tricky. However, its ability to have a flexible card format is unparalleled. I’ve tried a few plain-text-based alternatives like Obsidian’s Spaced Repetition plugin, but they are not even remotely close to what I need.
I don’t use spaced repetition to replace traditional learning. In fact, it takes up only a small portion of my total learning time. One thing that’s right about the “common sense” in the STEM fields is that without understanding, flashcards are useless. You need to understand the materials first, and reading flashcards written by others is a really poor way to do that. Two corollaries follow:
- don’t memorize what you don’t understand
- prefer your own flashcards to other people’s flashcards, at least for fields that require deep understanding
But once I understand something, flashcards are effective to keep the understanding alive.
When I started making flashcards, I looked at many flashcard decks from other sources, such as Anki’s Shared Decks and Quizlet, for inspiration. I found that most decks floating around on the Internet are of poor quality. They are usually definitions and facts semi-mechanically transcribed from a textbook.
I do something different. Most of my cards are handwritten by me and accommodate my brain.
While I have definition and fact cards, I also have many cards on intuition and “A-ha moments”. Those fade from memory, too, so it’s worth preserving them. Here is an example (feel free to skip if you are not familiar with the topic, but I intentionally picked something that I hope is easy to understand):
Q: What is the intuition that two reflections gives a rotation?
A: Both reflection and rotations are orthogonal transformations. The difference is that rotation preserves orientation while reflection flips it. If we apply the reflection twice, the first reflection flips the orientation and the second reflection flips it back. Also, if we apply multiple orthogonal transformations, the combined transformation is still orthogonal. Thus, at the end we get an orthogonal transformation that is orientation-preserving, which is a rotation.
See:
I add images whenever I can, and I often link back to the source materials where I learned the topic, in case I want to revisit. I also tie the flashcard-making habit with my note-taking habit. For example, the above card example is directly the result of the note on two reflections give a rotation in my digital garden.
Spaced repetition is not just for memorization; it can probably be viewed as a scheduled, recurrent task. So I put in things that people might not consider appropriate for flashcards. For example, I have a deck for math problems that I did wrong in the past. I use this basically to schedule practices. I put them into a separate Anki deck because I can only practice math with pen and paper, and definitely cannot do it outside.
The “recurrent tasks” perspective also gives me another insight: each card is a burden, so don’t be afraid to delete cards you don’t need. I generally spend around 1 to 30 minutes reviewing old Anki cards per day, depending on how many cards I added in previous days. I want to keep it as lightweight and low-overhead as possible, and that’s the only way I can keep this habit.
Nevertheless, the little time spent reviewing cards (and much more time writing them) is already worthwhile. I often pick up learning projects like a book and an online course, get busy with life, and pause them for a year. I used to forget everything. Now, after a year, I can still just pick up where I left off. How cool is that?
Is this all just illusion and confirmation bias? I don’t know. People are notoriously bad at judging their own learning and productivity. While there is an abundance of evidence on spaced repetition, the empirical evidence on Anki specifically is thin and drawn mostly from studies of medical students rather than from STEM fields. However, we make decisions with imperfect knowledge all the time. For me, this one has been worth it.
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