Or more elegantly put, what a door with two handle affords (An affordance is a quality of an object, or an environment, that allows an individual to perform an action – Wikipedia).
This has to do with an annoyance I have had for quite a while and that is, why are there doors with handles on both sides? Think to yourself, how many doors have push/pull signs? In my opinion much too many considering if a simple design change was implemented they could be done away with and there would never be any question which way a door goes
Currently those doors that have handles on either side afford for a user to either push or pull. If all doors were designed such that one side had a handle on one side did not, it would be very simple because it would be known that the handle is the pull side, and the other is the push side!
Because of this poor design I have actually created my own heuristics to avoid embarrassingly walking into a door (and yes I definitely have walked into one of these doors). If I am uncertain whether it is push or pull, I’ll put my hand on the handle and push in slightly (it is only noticeable if you know what I am doing) and if the door does not budge, I proceed to pull it. I personally think it is a little ridiculous that I have had to come up with a best practice to open a door!
This may be a rather trivial example, but these type of affordance problems can be seen anywhere, whether physical or in software/the web. A (contrived) web example could be a text box that you cannot type in that has a white background. A white background usually indicates that the text box can be typed in, and if the user attempts to type in it and they cannot they will be surprised. Despite the contrived nature of the above the example, it was meant to get you thinking about the software that you use and design affords. It is important in design to always be aware of what a given design affords, if there is any question about what it affords, I can guarantee you that someone is having trouble using it.
So go ahead look around at any physical or software design and think about what it affords, you may be surprised at what you discover.
–Steve