"A philosophy teacher is standing in front of his class.

He puts a big cup on the table and fills the cup up with a few rocks and asks his class: "Is this cup full?"

They reply "Yes".

So the teacher takes a handful of tiny stones and drops them in the cup and the tiny stones fall between the rocks into the cup and he asks: "Is the cup full now?"

Again everybody is mumbling "Yes".

Then he takes a hand full of sand and the sand goes between the rocks and the tiny stones and again he asks "Is the cup full now?"

Everybody answers "yes" again.

And he explains: "Those things are all symbols for something.

The cup resembles your life.

The rocks are the essential things of life, like your partner, your friends, your health.

The tiny stones resemble the important things of life, like your job, your other interests.

The sand resembles the extras in life, like a luxury car or a second house.

The philosophy behind it is this: You got to make sure you fill the cup that is your life with the essential things of life first, because if you fill it up with the extras - the sand - there is no room anymore for the rocks and the tiny stones."