Learn it the way
you'd learn to
ride a bike
.
Not by memorising definitions — by grabbing the thing and feeling how it moves. Start from zero; finish an expert, one rung of the ladder at a time.
- Free forever
- No account
- No ads
- Open source
- English + Español
Start from absolute zero
No jargon assumed. Course one assumes you have never met the subject before — and every later course only leans on the ones before it.
You poke it, not read it
Sliders, step-throughs, quizzes in every lesson. The idea moves when you move it, which is the difference between "I read that" and "I get that".
It doesn’t stop at “intro”
Most explainers tap out right after the basics. These keep climbing, all the way to expert depth, until the advanced stuff is just stuff you know.
Every course stands on the one below it.
Most sites give you scattered explainers. This is a single dependency graph: each course only assumes the ones before it, from the very first idea all the way to expert depth. You are never expected to know something you weren't taught.
- Beginner 1/412 courses
The absolute basics — no prior knowledge assumed, every term defined on first use.
- Intermediate 2/412 courses
The working vocabulary and the ideas the rest of the path leans on.
- Advanced 3/420 courses
Real depth, assuming the earlier rungs are behind you.
- Expert 4/428 courses
The deepest, most rigorous tier — practitioner-grade, all the way to the edge.
The full map lives in the catalog — a real dependency graph you can follow course by course.
72 courses. This is all of them.
From the very first idea to the deep end — every chip below is a full course you can open right now.
Built on how memory actually works.
Reading feels like learning; it mostly isn't. Every lesson here forces the three things that do work: predict, interact, retrieve.
- 1
Guess before you’re told
Lessons open with a question you can’t answer yet. Committing to a guess first is what makes the real answer stick — it’s the testing effect, and it’s built into every lesson.
- 2
Grab the idea
Every core concept ships with a slider, animation or step-through. The idea isn’t a paragraph here — it’s something you bend with your own hands.
- 3
Prove you got it
Quizzes, concept matchers, fill-in-the-blanks and spot-the-trap questions — varied on purpose, spaced through the lesson, never a wall of MCQs at the end.
- 4
Pass the final
Each course ends in a graded final exam: one shot per question, no retries, score at the end. Progress saves on your device — no account, ever.
Curated tracks, not one giant list.
Pick the area you care about and follow the graph from beginner to expert — or jump straight to the course you need.
Foundations
Start here. What a mental model is, the latticework idea, and the base models everything else builds on — map vs. territory, first principles.
Decision-Making & Judgment
Choosing well under uncertainty: inversion, second-order thinking, opportunity cost, margin of safety and expected value.
Probability & Uncertainty
Thinking in odds: base rates, Bayesian updating, regression to the mean, fat tails and sample size.
Human Nature & Bias
How minds misfire: the major cognitive biases, incentives, social proof and commitment & consistency.
Systems & Feedback
Wholes over parts: feedback loops, stocks & flows, bottlenecks, emergence and leverage points.
Economics & Markets
Incentives at scale: supply & demand, comparative advantage, externalities and the tragedy of the commons.
Problem-Solving
Cracking hard problems: first principles, inversion, thought experiments and Occam’s & Hanlon’s razors.
Science & Engineering
Borrowed from the hard sciences: critical mass, equilibrium, leverage, compounding and algorithms.
Biology & Evolution
Models from life itself: natural selection, adaptation, ecosystems and niches, and the Red Queen effect of constant co-evolution.
Strategy & Competition
Winning repeated games: game theory, moats, comparative advantage and the Red Queen effect.
Start at zero. Finish an expert.
72 courses, 508 lessons, one ladder — free, no account, in English and Spanish. It takes about ten seconds to start.