A teacher once told me about a student who couldn’t walk and
chew gum at the same time. He didn’t mean it literally, of course; it was a
comment on the student’s intelligence. We assume the smarter a person is, the more things they are capable of doing at the same time.
A juggler keeps multiple balls in the air simultaneously.
It can be impressive to watch a skilled multi-tasker at work. But human beings
have upper limits on our juggling ability. The maximum number of items ever
juggled is either 13 or 14, depending on who you believe. The case has been
made that the laws of physics make juggling 15 items impossible. At least, nobody
alive can do it.