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
afterward. 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?".