A philosophy professor stood before his class and had some items in front of him. When the class began, wordlessly he picked up a large empty jar and proceeded to fill it with rocks, about 2" in diameter. He then asked the students if the jar was full? They agreed that it was.

So the professor then picked up a box of pebbles and poured them into the jar. He shook the jar lightly. The pebbles, of course, rolled into the open areas between the rocks. He then asked the students again if the jar was full. They agreed it was. The students laughed.

The professor picked up a box of sand and poured it into the jar. Of course, the sand filled up everything else. "Now," said the professor, "I want you to recognize that this is your life. The rocks are the important things - your family, your partner, your health, and your children - things that if everything else was lost and only they remained, your life would still be full. The pebbles are the other things that matter like your job, your house, and your car. The sand is everything else: the small stuff. If you put the sand into the jar first, there is no room for the pebbles or the rocks. The same goes for your life.  If you spend all your time and energy on the small stuff, you will never have room for the things that are important to you. Pay attention to the things that are critical to your happiness. There will always be time to go to work, clean the house, give a dinner party and fix the disposal. Take care of the rocks first - the things that really matter. The rest is just  sand. 

But then... a student took the jar which everyone agreed was full, and proceeded to pull a bottle of wine out of his knapsack and pour it in the jar.  Of course the wine filled the remaining spaces within the jar making the jar truly full.