When we interact with everyday objects, we have an expectation of how they are going to work. This is known in design as affordance. For example, if you see a handle on a door, it should be instinctive to you that you should be pulling on the handle; conversely, a flat rectangular piece of metal (called a finger plate) attached to the door implies it should be pushed:
(Left) Adding a handle to the side of the door that is meant to be pushed is an example of bad design, as the handle is for pulling, not pushing. (Right) The handle already suggests that the door is meant to be pulled, so the "Pull" label is unnecessary here. This image ...
