Why twenty minutes a day beats one long night
A single card, forty-five days of calendar, and the algorithm behind Anki reduced to three buttons. Watch what one well-timed review does to the forgetting curve, what a lapse takes away, and why the whole deck becomes cheap only once the intervals have grown.
Stage Forgetting
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Tap a stretch of the calendar to open that stage.
The schedule is not motivation, it is arithmetic
Spaced repetition does not make you study more, it makes each review buy more. One well-timed answer multiplies the interval instead of adding to it, and once the intervals have grown, a deck of several hundred questions costs a few minutes a day. The only thing that breaks it is reviewing everything every day, which feels like effort and is mostly waste.
What's inside
- 1 A road sign learned once is gone in a couple of days — The curve is a plain exponential, retention as the elapsed days divided by the current stability. It is a model, not a measurement of your memory.
- 2 One review at the right moment does two things at once — Reviewing earlier than due is close to free; the stretch comes from recalling something that was genuinely about to slip.
- 3 From there the interval is multiplied, not extended — Ease is a per-card number. Cards that keep being easy drift upwards, cards that keep being hard drift down, and the schedule separates them without you deciding anything.
- 4 Forgetting once costs the interval and a slice of the ease — The ease has a floor. A card you keep failing settles into short intervals rather than falling forever, which is how the hard ones stay in rotation.
- 5 The saving is the average interval, and nothing else — At fifteen seconds a question that is the difference between a bus ride and most of an evening, every day, for the same result.
Explorable Explanations
- Reading an exam question in a language you are still learning One real question from the Argentine theory bank, taken apart the way a learner actually meets it. Most of the words can be guessed or skipped. The two that cannot are the entire question, and a full translation hands you the answer while hiding which word carried it.
- How much clear road an overtake actually needs You are behind a truck doing seventy, you can see three hundred metres of road, and there is a car coming the other way at the far end of it. The manoeuvre only works if your path and its path fit inside the same stretch. One slider sets your speed; the overlap on screen is exactly how much you are short.
- Who goes first, and why it is almost never the right-hand rule One street, four junctions: an uncontrolled crossroads, a priority road, a green light and a roundabout. The same two cars meet at each of them, and the answer changes three times. The slider drives the route, and the tally at the end counts how often the habit everyone remembers gets it wrong.
- Why stopping has so little to do with the brakes Something blocks the road a hundred metres ahead. Whether you stop in front of it, or reach it and at what speed, comes down to two distances that behave nothing alike: one grows in step with your speed, the other with the square of it. Two sliders, one road.
- How a search engine decides who gets found Ten blue links look like a list. They are the last frame of a pipeline that starts with a crawler and ends with a click curve. One slider walks the whole thing.
- How a generated answer picks the sources it will name An answer engine does not rank pages. It writes a paragraph and then decides which pages to credit for it. One slider follows a single question from fan-out to citation.
- One page, two front doors SEO and GEO are not two projects. They are one document that has to satisfy two different readers: a ranking function and a retrieval step. One slider shows what they share, what they don't, and what it costs to add the second door a year late.
- How a drug is smuggled past the blood–brain barrier The brain refuses almost every drug molecule, and it is right to. One slider follows the trick the labs are trying instead: wrap the molecule in a bubble the wall already knows how to carry.
- How a robot draws the map of a room it has never seen A lidar returns a few hundred dots per sweep and no idea where it is. One slider walks from that cloud to a floor plan with the robot standing in the right spot.
- How two people type in one line without losing a letter Two cursors, one line, nobody holding the pen in the middle. One slider takes an index-based merge apart and rebuilds it out of addresses that sit between the letters.
- Why a quantum computer stops at a lattice Shor’s algorithm eats RSA in one move. The same machine gets almost nothing on a grid of points with a little noise added. One slider shows the difference.
- Cooling a building by pointing it at space A coating that stays colder than the air around it, in full sun, drawing no power at all. One slider follows the heat from the sun to the far side of the atmosphere.
- How a robot predicts the next second A text model guesses the next word. A world model guesses the next frame — mass, speed and gravity included. One slider walks the whole loop, from the camera to the catch.
- Proving a secret without revealing it One slider walks through the stages, the other adds rounds. Watch certainty climb to almost total while the secret stays a secret.
- Getting lithium out of brine: ponds versus direct extraction Move the slider through five stages and compare two ways of taking the same metal out of the same salt water.
- How a personalised mRNA cancer vaccine works Move the slider through five stages and watch how a tumour’s own mutations become the instructions that teach the immune system to find it.
- The edge of the app Everything arriving from outside is untrusted. Break one link at a time and watch where the chain stops and what the screen shows.
- How search over your documents works Move the sliders and watch a search pipeline decide what the model is allowed to see — and what happens when it is fed the wrong passage.
- Retries and slow responses The network drops in the middle of an operation. Press the button twice and see what ends up in the database — with an idempotency key and without one.
- How a language model writes The weights are frozen and nothing is remembered. Pull the sliders and watch the model pick the next piece of text, over and over.
- How a language model learns Pull one slider and watch a pile of random numbers turn into a prediction over a thousand training steps.
- Where electricity comes from Pull one slider and follow the energy from a river all the way to a pump that lifts water back up.