Cap Simultaneous Motion
SHOULD: With 3+ elements, keep at most ~1/3 in active motion at any instant so the eye keeps an anchor: land a hero element first, then bring the rest in waves. This is NOT stagger — stagger sets when items START, this caps how many are MOVING. A 30ms stagger over 9 cards with a 220ms duration still has all 9 in flight; you need both rules.
Keep no more than a third of a group in active motion at any instant so the eye keeps an anchor
Bad
Good
Why it matters
Nine cards that all scale, fade and slide on mount give the eye nothing to hold on to: the grid is perceived as a burst of noise that resolves, not as a reveal you can follow. Land a hero element first so there is an anchor, then bring the rest in waves — with a 220ms per-card duration and waves at 0/200/340/480ms, at most 3 of 9 are ever in flight and the cascade still finishes inside the 500ms stagger budget.
DISTINCT FROM animations-emil-stagger, which prescribes a per-item DELAY (30–80ms) and says nothing about how many items overlap: a 30ms stagger across 9 cards with a 220ms duration still has all 9 moving at the same time, because item 9 starts at 240ms while item 1 is still animating. Stagger controls when things start; the 1/3 rule controls how many are moving at once. You need both, and satisfying one does not satisfy the other.