Designing something a stranger will play for twenty seconds, without instructions, on a screen they are holding one-handed, while waiting for something else to resume, is a genuinely hard brief. It is closer to designing a toy than an advertisement.
The pieces in this section are about the decisions inside that brief: what to teach first, what to cut, how much feedback an action needs, and when to stop. Most of them come down to restraint — the common failure is not too little ambition but too much of it in too little time.