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 ClassiCCautionary tale to human-faCtors designers "Remember the gorilla arm!" is shorthand for "How is this going to fly in *real* use?".