A professor once took a big glass jar and put a few big stones into it, until it was full. He then asked the students if the jar was full. They replied Yes. Then he put in a few pebbles, shook the jar and the pebbles settled in. Then he asked his students again if the jar was full. They replied Yes. Then he took some sand and put it into the jar and repeated his question. The students answered Yes. Now if you had filled the jar with sand first, there would be no space for anything.
Now consider that the jar is your life. The big stones are your important things, family, partner, health and children. And consider the small stones were your job, car, etc. all the material things of life, not as important as the big stones. If only the big stones were in your life, it would still be considered full. But if you realize we fill our lives with small stones and sand first, stressing on everything small and not as important in our lives. Take care of the big rocks first and set your priorities in life.