YouTube is not built to teach you.

1. 01

   Extra material makes you learn less

   The coherence principle holds that people learn better when related but non-essential material is removed — not merely that they prefer it. Interesting extras compete for the same working memory the lesson needs.

   Mayer, Cambridge Handbook of Multimedia Learning

   In practice no sidebar of unrelated videos while you watch. The only thing beside the player is the rest of your playlist.

2. 02

   Switching leaves a residue

   Attention residue: after you switch away from a task, part of your attention stays behind, and performance on the next task drops. A "quick look" at a recommended video is not free — it is charged to the thing you were learning.

   Leroy, 2009, Organizational Behavior and Human Decision Processes

   In practice nothing on a watch page is designed to pull you off it.

3. 03

   Your attention has a hijack button

   The brain runs two attention systems: a goal-directed one you steer, and a stimulus-driven one that reorients you automatically toward anything abrupt or salient. A wall of high-contrast thumbnails is built for the second system, and it does not ask the first for permission.

   Corbetta & Shulman, 2002, Nature Reviews Neuroscience

   In practice you pick a subject, then an area, then a playlist. Every step is a decision you made.

4. 04

   Unpredictable rewards are the stickiest

   Under a variable-ratio schedule — where the payoff comes after an unpredictable number of tries — behaviour becomes both fast and very hard to extinguish. A feed where most videos are mediocre and the occasional one is superb is exactly that schedule.

   Ferster & Skinner, Schedules of Reinforcement

   In practice there is no feed to pull. The catalogue is finite and someone vetted it.

One more, on the positive side: distributed practice — spacing material out and returning to it — reliably beats cramming it into one sitting (Cepeda et al., 2006, Psychological Bulletin). An ordered playlist you can leave and come back to is built for that. An endless feed is not.