Check that you really understood — Tutorial to Engineer

1. The habit

After you try something and it works, don't move on yet. Stop. Ask:

If a friend who didn't know this asked me to explain it tomorrow, could I — without going back to the materials?

Not would I remember the name. Not could I find the docs. Could I explain it, with examples, in my own words, while looking them in the eye.

If yes, you have it. If no, you don't — you had it for the duration of the task, and that doesn't count.

2. Why "teach it" is the test

Teaching forces compression. You can't explain something you don't have a clean mental model of, because explanation requires picking out what's essential from what's incidental. Anything you've been holding fuzzily collapses the moment someone says wait, why?

This is why teaching is one of the most efficient ways to learn — not because you give it to someone else, but because the act of preparing to give it audits what you have. Most things you "know" don't survive the audit. That's information.

3. The cheap version

You don't actually need a friend on demand. The cheap version of the test is: write down the explanation, in two paragraphs, as if explaining to a junior on your team.

Or — even cheaper — explain it out loud to the wall. Yes, really. The rubber duck works. If you stumble in the third sentence, that's where your understanding ends.

4. Try it

Pick the most recent thing you "learned" — a concept, a pattern, a snippet you made work.

Explain it here, in your own words, as if to a colleague who's never seen it. Stop when you stumble — that's where the gap is.

Where you stumbled is the next bite. Loop the loop on just that.