Today, as a museum gallery host, I watched a design failure - I'm confident it was unintentional - unnecessarily block access to one of the exhibits. I think it was because of a certain way the design team was all alike.
It was a mock 1920's telegraph, attempting to highlight communications from a small town that did not yet have telephone service. It has a vigorously ruggedized mock telegraph key for the guests to try using morse code to spell out messages. When pressed firmly, it sounds a buzzer so the guest can hear the dit-dah patterns of morse code. It has the same functionality as Morse code trainers had in the era of morse-using telegraphs. The one at the link has a key, a copy of the Morse code version in use at that facility, a buzzer, and a light.
But it doesn't have the light. Maybe it was ruggedization decision. Maybe they tried it in quiet rooms. I'm sure it worked great. I am guessing, from the evidence of how the exhibit failed, that all the designers and testers were hearing.
But when a Deaf, hard of hearing, and guests with auditory processing difficulties try to use it in a busy exhibit, next to classes of kids and audio/video materials playing on the wall: it fails. There's only audio feedback, unlike the one shown above.
So I'm going to try to make a better one, Step one: try to figure out my "blind spots" that are already built into the existing one, so I don't remove functionality. Important functionality, like no exposed wires, can't be put in a backpack, is not permanently damaged by three-year-olds that use it as a climbing wall (or teens that just don't want to be there), has a label that can be read from a wheelchair (even if the guest has limited vision), and can be understood by ... um... everyone?
That's the hard part. I can read lots of requirements to get ideas about access for different parts of the audience, and do a first approach that way. But without a really diverse group telling me what's wrong, I'm gonna fail in ways I don't yet know.
So I better put plans in it somewhere, so the next person can build on my build.