Big and Close
Paul Fitts published the law in 1954: the time to acquire a target depends on its size and distance. Seventy years later it still governs every button, link, and tappable region in every interface anyone has ever shipped.
The time to point at a target grows with distance and shrinks with target size — logarithmically. Double the distance, and time goes up by a constant. Double the width, and time falls by the same constant.
Increase W and pointing time drops — fast. The biggest, most-used controls should be the largest controls. The CTA isn't ornament; size is function.
Distance increases pointing time logarithmically — meaning the cost of moving across a screen is real. Place the next action near the last one. Don't make the user travel.
Small AND far is the slowest possible combination. Most accidental clicks happen here — a tiny "close" icon at the opposite corner of the screen from where the eye and pointer already are.
The cursor can't move past a screen edge, so any target placed against the edge effectively has infinite width along that axis. The Mac menu bar is faster than every dropdown in Windows for exactly this reason.
A corner is infinite in two dimensions. The cursor slams to a stop in both axes regardless of overshoot. Start menus, close buttons, and macOS Hot Corners exploit this — the fastest possible click on the screen.
A circular menu places all options at the same distance from the cursor — and the slice's angular width becomes effective target size. Mature users can build muscle memory for direction, not destination.
A small icon can have a much larger invisible hit area. Extending the clickable region with padding makes the visual element tidy and the actual target generous — a free Fitts's-Law upgrade.
On touchscreens, the "cursor" is a finger pad — roughly 9–10mm wide. Apple recommends 44pt minimum, Material 48dp. Below that and accidental taps spike; the fastest UI becomes the most frustrating.
Moving the cursor through a narrow corridor (cascading submenus, nested context menus) is dramatically slower than hitting an open target — the steering law extends Fitts's into paths. Slipping out of the tunnel resets the user.