Fitts's Law is an ergonomic principle that ties the size of a target and its contextual proximity to ease of use. In other words, if a tool is close at hand and large enough to target, then we can improve the user's interaction. Putting tools in context makes for lightweight interaction.
Fitts's Law:
The time to acquire a target is a function of the distance to and size of the target. It is proportional to the distance to the target and inversely proportional to the width of the target.