Origins
In 1954, psychologist Paul Fitts, examining the human motor system, showed that the time
required to move to a target depends on the distance to it, yet relates inversely to its size. By his law,
fast movements and small targets result in greater error rates, due to the speed-accuracy trade-off. Although
multiple variants of Fitts’ law exist, all encompass this idea. Fitts’ law is widely applied in user
experience (UX) and user interface (UI) design. For example, this law influenced the convention of making
interactive buttons large (especially on finger-operated mobile devices)—smaller buttons are more difficult
(and time-consuming) to click. Likewise, the distance between a user’s task/attention area and the
task-related button should be kept as short as possible.
Source