When the old master Hyakujo was asked what Zen is,
he said -
"When hungry, eat. When tired, sleep."

His questioner countered -
"Well isn't that what everybody does? Aren't you just like ordinary people?"

"Oh no," he said, "they don't do anything of the kind. When they are hungry they don't just eat, they think of all sorts of things. When they're tired they don't just sleep, but dream all sorts of dreams."