Measurement

Hey kids!  The emperor and his kingdom are having a problem with measurement.  Can you help them figure out what to do?

    Once upon a time there lived a greedy emperor.  Although his people paid taxes every year, he still wanted more, so he decided that each person living in the emperor's town would be required to bring 4 bags of wool for the emperor to make clothes out of for himself.

    One by one the emperor's people began bringing four bags of wool to his palace and they were very proud to have been able to satisfy the emperor's wishes.  The first man to arrive was carrying four bags of wool.  These weren't just any bags, they were huge garbage bags full of wool!  The emperor was impressed and thanked him graciously and the man went on his way. 

    The second man came to the palace with four bags of wool.  These weren't just any bags, they were four plastic sandwich bags full.  The emperor saw the man's four tiny bags and turned him away to get more.  Why did the emperor turn the second man away?  Didn't the man do exactly as the emperor had asked by bringing him four bags of wool?