This teaches you the difference between animation that works and animation that feels alive. The core insight is subordination: secondary actions like a button's ripple effect or a character's arm swing must enrich the primary motion without competing for attention. You get practical amplitude guidelines (10-20% for professional interfaces, 50-60% for games), the crucial distinction between secondary and overlapping action, and the "remove and test" method to validate your choices. What's valuable here is the implementation heuristic at the end: for every primary action, ask what else would be moving, add the single most valuable secondary action, then time it to offset from the primary. It's the kind of framework that stops you from either over-animating everything or leaving interfaces feeling dead.
npx skills add https://github.com/dylantarre/animation-principles --skill secondary-action-mastery