There was an old lecturer who taught his students "effective time planning". In the course of the lecture he conducts an experiment in front of a hall filled with students filling a glass container on the table with large stones. When a larger stone could not enter the tank, he turned to his students and asked, "Is the container full?"
"All the students answered, yes, the tank is full." The lecturer proves that the answer is wrong when he inserts pebbles in the tank that fill the gaps, the pebbles infiltrated between the large stones until they reached the bottom of the tank.
Then the lecturer turned to his students and asked, "Is the container full?" One of the students replied, "Probably not." "Right," replied the old professor so that the lecturer repeated his actions and put sand and then water to block any empty space in the tank.
To the question of what a great truth can be learned from the experiment, one of the students answered: "We learn that as our diary seems to be full of tasks and commitments, if we try, we will always find more." "No," replied the old professor.
"Not that, the great truth that the experiment proves to us is that if we do not put the big stones first, we will never be able to insert all the stones afterwards."
The old man looked at his listeners and said, "What are the big stones in your life? Your health? The family? Friends? What do you like to do? Fight for a higher cause? ... What you must remember is that it is important to insert the large stones first. If you do not forget to ask yourself what are the great stones in your life and you will find them, put them into your container.