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 right to the top; rocks about 2" diameter.
The professor then picked up a box of pebbles and poured them into the jar.
He shook the jar lightly.
The pebbles rolled into the open areas between the rocks.
The professor then picked up a box of sand and poured it into the jar.
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. Anything that is so important to you that if it were lost, you would be nearly destroyed. The pebbles represent things in life that matter, but on a smaller scale. The sand is everything else. The small things in life.
If you put the sand or pebbles into the jar first, there is no room for the rocks. The same goes for your life. If you spend all your energy and time on the small things, the material things, you will never have room for the things that are truly most important."