After filling an empty disposable paper cup with stones, he took out a box of pebbles and poured them into the disposable paper cup, and gently shook the disposable paper cup to let the pebbles roll into the space between the stones. Then the professor took out a box of sand and poured it into the disposable paper cup, shook the disposable paper cup to make the sand fill all the gaps, and finally poured water into the cup until the water penetrated into the sand and overflowed the edge of the cup. After that, the professor said to the students, "now, I want you to understand this disposable paper cup as life. The stones in it represent the most important things in life, such as family, partner, health, children, etc., all of which are very important to us and will never be made up once lost; the pebbles represent the more important things in life, such as work, house, car, etc.; the sand represents the daily trifles in life; the water represents worry and depression. If we put water and sand in disposable paper cups first, there will be no room for stones and pebbles. "