Fitts’s Law
Targets are faster and easier to reach when they are larger and closer to the starting point.
A control is not easy to use if it is easy to miss.
A tiny close icon sits in the corner of a dialog. The symbol is visible, but its clickable area is almost the same size as the mark. The person aims carefully, misses, and tries again. The problem is geometry, not attention.
Origin
Paul Fitts published his model of rapid aimed movement in 1954. Movement time rises as the target becomes farther away or narrower along the direction of travel.
Make the hit area larger than the visible icon when space allows. Padding can improve targeting without making the symbol visually louder.
Place frequent or sequential actions near the current point of attention. Reducing repeated travel can matter as much as enlarging the target.
Leave enough space between risky actions. A large target is not safe if a nearby destructive control catches the same imprecise movement.
Test with touch, mouse, keyboard, zoom, and reduced dexterity. The effective target depends on the input method and the person using it.
Digital systems
A forgiving icon button
The close icon stays visually compact, but the full padded button accepts the click. The larger hit area improves selection without changing the layout's hierarchy.
Physical signals
An emergency stop button
A large, raised control is easier to strike quickly than a small flush switch. Its size and separation support action when precision is limited.
Small targets, long pointer travel, and crowded controls slow the action and increase the chance of selecting the wrong thing.
Increase the interactive area, reduce unnecessary travel, and separate competing actions so people can move quickly without giving up accuracy.