Okay, not an adventure. Last year, during a layover at the Heathrow Airport, I had occasion to visit the washroom. The fixtures looked familiar, as they do almost everywhere, but they gave me trouble. I couldn't figure out how to turn the water on.
Rotating the lever toward me and away from me didn't help. Waving my soapy hands under the tap did nothing more than make me feel silly.
In the end, I just waited. Not for the water to come on, but for someone else to use one of the basins nearby. Aha! You simply pull the lever outward, to the side, and it works.
This is an awkward story to tell to my students. In short form, I went into a public lavatory, stood around watching people, and eventually took a few pictures with my camera... The things I do for the sake of education.
(As an aside, students do find the subject of usability in private settings interesting. For some years I asked students in my classes to send me descriptions of design problems they encountered in their everyday lives. A good number of their stories concerned bathrooms, public and private.
(One student described her bathroom at home, with a mirrored medicine cabinet over the sink. At a friend's house she found a similar set-up. When she pulled on the edge of the mirror, though, she discovered--as it crashed into the sink--that it wasn't a cabinet after all.
(Other students objected to having to pull open a door when leaving a public bathroom; to stalls that are too small, with inward opening doors and very little clearance; to infrared sensors that are too sensitive or don't work at all; to Braille signs reading "Men" and "Women" mounted above each door frame. The longest story was from a student whose brother was replacing the sink cabinet in the bathroom of his fraternity house. Alcohol was involved. The result was a cabinet that extended outward far enough to prevent the door from closing and a paper dispenser mounted was well out of reach of someone using the facilities.)
Important lessons about usability can be found in ordinary situations.
Visibility. Don Norman introduced this concept in his wonderful book, The Design of Everyday Things (1988), saying that "The correct parts must be visible, and they must convey the correct message." I explain it to my students as a property of the relationship between a physical (or software) control and its function: if the functionality is apparent by observation or through exploration, then we say that the function is visible.
The function of turning on the water in the Heathrow washroom isn't visible in Norman's sense. We see a lever that's designed to rotate in a vertical plane. Pulling it outward isn't the most obvious thing to do; in fact, there's even a slight resistance to movement in this direction, to ensure that the tap doesn't drip if the lever is slightly out of place. It takes knowledge to use the tap--easily acquired, but not obviously embodied in its design.
Computer interfaces sometimes have comparable problems. Buttons that don't look like buttons, so that it's not obvious that they can be touched or clicked. Gestures on a touch interface--how do I know what it's possible to do? Voice-based telephone systems in which a computer says a great deal but understands very little. Entire books could be be written about visibility problems in interactive software.
Affordance. James Gibson gave a definition in The Ecological Approach to Visual Perception (1979):
The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill. The verb to afford is found in the dictionary, but the noun affordance is not. I have made it up. I mean by it something that refers to both the environment and the animal in a way that no existing term does. It implies the complementarity of the animal and the environment.
Gibson argued that we "pick up" affordances effortlessly, by identifying invariants in our environments. I like the concept, in the abstract. It's very hard to pin down in concrete terms, though, and three decades of research in ecological psychology has not led to universal agreement even about what affordances are. Further, how affordances apply to the usability of software or physical devices isn't entirely clear. (Strictly speaking, if it's possible to do something, then that functionality is afforded, but this alone offers little guidance about how to improve usability.)
Learning by social interaction. (There are formal theories of social learning, but I'm talking informally.) When I started my first job as a software engineer, I worked on a computer--a Texas Instruments Explorer Lisp machine--that was accompanied by a dozen volumes of documentation. That's unheard of today. How do we learn to do something new? Sometimes we can simply ask: "How do I do this?" Sometimes it's more passive: you watch over someone's shoulder. And sometimes we do it without anyone around: to solve a problem I can type a description into a search engine and see what others have said.
Learning in this way is very common. You might have experienced it in formal ceremonies (I'd better stand up now, like everyone else), at social events (I guess I should go to the end of this line to get in), at the dinner table (this fork, not that one), and so forth. It doesn't happen very often in a public washroom, but I'll take when and where they appear.