I never completely understood table manners, particularly why there are virtual duplicates of utensils for different purposes, or what's the "appropriate" action to take to finish the last bit of soup in your bowl (I usually just tip it up and drink it). I do know that the "elbows on the table" rule stems from days long gone, where lower and middle class families would all have to sit on one side of the table in order for everyone to be served. If everyone leaned on the table, then it would tip over and spill the food all over everything.
Most of the things that don't occur to me are traditions done for the sake of tradition without any good or applicable reason nowadays. Right from wrong is fairly simple, but the vast gray area between them is what trips me up.