Protect the user's sense of speed

Why this rule exists

How fast an interface feels matters as much as how fast it actually is, because the user experiences the perception, not the milliseconds. A response that arrives instantly feels effortless; one that lags even slightly breaks the sense of direct manipulation and makes the whole product feel heavy. Much of perceived speed is design's job, not just engineering's: showing an immediate acknowledgment, updating the interface optimistically before the server confirms, revealing content progressively so something useful appears at once. Waiting is not just lost time; it is a small erosion of the user's momentum and patience, and momentum is fragile. The interfaces that feel delightful are often not the ones doing less work but the ones that hide the work well, keeping the user moving while the machinery catches up. Respecting the user's momentum means never making them stare at nothing when you could be showing them something.