One day an expert in time management was speaking to a group of business students and, to drive home a point, used an illustration those students will never forget. As he stood in front of the group of high powered overachievers he said, "Okay, time for a quiz." Then he pulled out a one-gallon, wide-mouthed Mason jar and set it on the table in front of him. Then he produced about a dozen fist-sized rocks and carefully placed them, one at a time, into the jar. When the jar was filled to the top and no more rocks would fit inside, he asked, "Is this jar full?"
Everyone in the class said, "Yes."
Then he said, "Really?" He reached under the table and pulled out a bucket of gravel. Then he dumped some gravel in and shook the jar causing pieces of gravel to work themselves down into the space between the big rocks. Then he asked the group once more, "Is the jar full?" By this time the class was on to him. "Probably not," one of them answered. "Good!" he replied. He reached under the table and brought out a bucket of sand. He started dumping the sand in the jar and it went into all of the spaces left between the rocks and the gravel. Once more he asked the question, "Is this jar full?"
"No!" the class shouted.
Once again he said, "Good." Then he grabbed a pitcher of water and began to pour it in until the jar was filled to the brim. Then he looked at the class and asked, "What is the point of this illustration?" One eager beaver raised his hand and said, "The point is, no matter how full your schedule is, if you try really hard you can always fit some more things in it!"
The point of the story with the rocks and the gravel and the sand and the water is NOT that you can always cram more in.
The point is that you need to put the big rocks in first.