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 mayonnaise jar and proceeded to fill it with rocks, rocks about two inches in diameter. He then asked the students if the jar was full. They agreed that it was. So the professor 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 professor then picked up a box of sand and poured it in the jar. Of course the sand filled up the empty spaces.
"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 children, your health - 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 house, your job, and your car. The sand is everything else. The small stuff. "If you put the sand in first there is no room for the pebbles and rocks". The same is true with your life".
But then a student took the jar, which the professor and the other students had agreed was full, and poured a beer into it, and the beer soaked into the sand filling the jar completely. Proving that no matter how full your life is there is always room for a beer.