An affordance provides insight, without the need for explanation, into how something should be used. In contrast to a constraint that limits the actions possible, an affordance provides visual (or other sensory) prompting for the actions that should be performed. Once we see the fixtures on a door, we should be able to determine whether it opens in, opens out, or slides. There should not be a need to refer to labels or to use a trial and error approach. If a process or product can be designed to lead the user to perform the correct actions, fewer errors will occur.