The feeble of the professor who filled a jar with rocks, pebbles and sand is a famous one. In the story, a professor fills a large jar with big rocks. He then asks his students if the jar is full; they say yes! The professor then pours pebbles into the jar, which fills the gaps between the rocks. The students again agree that the jar is now full. Finally, the professor pours sand into the jar, which fills the remaining gaps.
The experiment is not possible if you start with sand. The story's moral is that if you don't prioritize the big rocks (the essential things in your life), you may not have enough room for them later. The space could be any resources but most obviously it represents time you have. You'll be too busy with the small pebbles and sand (the less important things) to make time for the things that matter most. Therefore, it is essential to prioritize your time and focus on the most important items first.
As fascinating as that feeble is, I have had some problems with it.
I am not sure what my rocks are!
The story assumes that people can easily distinguish between their big rocks and the less important things, which may only sometimes be accurate. I mean there are some obvious rocks; my family, health etc. But there are other rocks in life; I mean when I was doing my USMLEs, I sort of had to prioritize studying over many other rocks. Is my dream job a rock or a pebble?
What about the rocks the professor did not put in the jar?
The professor either brought in an exact number of rocks that could fit in the jar or left some outside. Had he brought in more rock, no matter the sequence, he could not have fit them in the jar. What rocks do I leave out? What are those important goal in my life that I prioritize over other important goal in my life? One solution I can think of is being honest about the size of the jar to oneself. I have finite resources and infinite desires. My decisions better be conscious. I can watch youtube shorts for 2 hours but I better know that I am filling in the jar with sand. YouTube shorts can probably be a pebble to someone, although I find that hard to imagine.
The other solution that may work in tandem with the first one is to be intentional about your rocks. Examine your rocks frequently. Is getting into that particular school/field/subject/residenty/fellowiship/country a rock?