You're on a roll today. Sigh, no, if everyone took the the elevator all the time we wouldn't lose the ability to go up stairs. Not unless we flattened the entire planet and even then, no, we wouldn't. Your above example regarding the change isn't a mental math error, they did actually perform the correct calculation for the figures they had, they just weren't paying attention, with or without too much reliance on calcalators they would have blown it....I think humans have been spacing on shit since the beginnnig of time.