The side-effect that destroyed touch-screens
as a mainstream input technology despite a promising start in the
early 1980s. It seems the designers of all those spiffy
touch-menu systems failed to notice that humans aren't designed to
hold their arms in front of their faces making small motions.
After more than a very few selections, the arm begins to feel sore,
cramped, and oversized -- the operator looks like a gorilla while
using the touch screen and feels like one afterwards. This is now
considered a classic cautionary tale to human-factors designers;
"Remember the gorilla arm!" is shorthand for "How is this going
to fly in real use?".
