Can you guess what these signs, found near elevators, mean?
Getting in the wrong elevator, a friendly Korean explained I was in the odd-numbered elevator and I would have to go all the way down and switch elevators. Nothing in the elevator gave me a clue why pressing buttons had no effect whatsoever. No beep, no light, nothing.
Not one but two hostels were located in this Seoul high-rise, so hundreds of functionally illiterate people were confronted with these signs. Many were also sleep-deprived and jet-lagged.
"Don't Make Me Think" is a solid usability principle. I'll add a more specific one: "Don't assume literacy".
The signs on 1st floor elevators were slightly better:
Green is good colour to denote "go" like in traffic lights, and the numbers on the signs are different, letting you guess meaning. Crossed out numbers where it didn't stop could have helped.
Simpler would be to just have both elevators stop everywhere. No sign, no explanation. Just get in and press the button for your floor.
Something even an illiterate person can understand. Which I really appreciate when that person happens to be me.