How learning decay works

In the 1880s, the psychologist Hermann Ebbinghaus memorized lists of nonsense syllables and tested himself at different intervals afterward. What he found has held up in study after study since: we forget fast at first, then more slowly. A big share of new material is gone within days if nothing brings it back.

The dashed line is what happens when you learn something once and move on. The gold line is the same material, reviewed three times. Each review lifts it back to the top, and, just as important, each one makes the next drop slower. That’s why the gaps between reviews can keep getting wider.

Three habits make the biggest difference, and Orivian is built around all of them:

• Retrieval, not rereading. Pulling an answer out of your head strengthens memory far more than looking at the material again. That’s why reviews are questions, not slides.
• Spacing. Reviews spread over days and weeks beat the same time crammed into one sitting. Short and often wins.
• Variety. Seeing the same idea from different angles builds understanding you can use on exam day. Answering the exact same question again mostly tests whether you remember the answer.

With Retention mode on, every lesson you’ve passed gets a retention score, an estimate of how much of it you’d still recall today. It’s driven by one number, the lesson’s half-life: how long it takes for retention to drop by half.

1. 1You pass a lesson. Retention starts at 100% with a 7-day half-life.
2. 2Time passes. Retention halves every half-life: about 50% after 7 days, 25% after 14.
3. 3You pass a review. Back to 100%, and the half-life doubles (7 → 14 → 28 → 56 days, up to 120). Retakes crammed back-to-back refresh it but don’t grow it, so space them out.
4. 4You miss a review. The half-life halves (never below 2 days), so it comes back to you sooner.
5. 5You go quiet. From the 3rd day in a row without a lesson, each idle day counts as 1.5 days of decay.

Each lesson then sits in one of three states on your trail map:

When two or more lessons in the same section fade, that section’s flag turns frost blue on your trail. That flag is a review waypoint: click it to start a review session for that section. Your course page also lists the lessons to review first, weakest at the top.

Your streak calendar shows warm days, when you completed a lesson or a review session, and cold days , when you didn’t. Cold days start after your first lesson. Today is never cold; there’s still time.

When you’re on a cold run, the flame in the menu turns to frost and counts the cold days instead. Complete a lesson or a review and it’s back to a flame. Missing days doesn’t cost you anything you’ve earned; the frost is just a nudge that the material is cooling off.

Retention mode is on for every course by default, because knowing what’s slipping is what makes the learning stick. But some people just want to work through a course at their own pace, so you can turn it off:

• For one course, with the Retention mode switch on that course’s page. You might keep it on for a certification you’re sitting next month and turn it off for a fun After Hours course.
• For all your courses, from your profile. Changing it there resets any course you’d set on its own.
• Turning it off only hides the fading. Your history keeps counting, so if you switch it back on you see an honest picture of what you still remember.

A review session is a short quiz for one section, built only from the lessons there that have faded: up to three questions each, from up to five lessons, so never more than ten. One faded lesson means a three-question review. The questions are mixed together, because switching between topics makes you work harder to recall each one. Start one from a frost flag on your trail or from your course page. There's no pass mark, and it counts as a warm day on your calendar.

• Least-recently-seen questions first. Each lesson's questions are picked by how long it's been since you last answered them. Bigger pools of review-only questions are being added course by course.
• Each lesson is judged on its own questions. All right: back to 100% and its half-life doubles. Some right: refreshed to 100% at the same pace. None right: it keeps its frost and fades faster, with a link straight back into the lesson. Each session covers up to five lessons, and your course page shows how many sessions it would take to clear a section.
• Just one lesson? You can also retake a single lesson's mini-exam. Passing it counts as a review too.