I asked people of different ages to answer the riddle. Children could see the answer almost instantly; teen-agers were a little slower but half of them could get the answer within five minutes; only a few thirty-year olds could see the answer within ten minutes; and sixty-year olds were almost never able to see the answer. When told the answer, the sixty-years olds would slap their heads in disgust and say, "Oh, of course. Why didn't I see this?" LOL. This experiment simply illustrated how habits of mind gradually obscure the obvious as we age.