A philosophy professor once stood before his class with a large empty mayonnaise jar. He filled the jar to the top with large rocks and asked his students if the jar was full.
The students said that yes, the jar was indeed full.
He then added small pebbles to the jar, and gave the jar a bit of a shake so the pebbles could disperse themselves among the larger rocks. Then he asked again, “Is the jar full now?”
The students agreed that the jar was still full.
The professor then poured sand into the jar to fill up any remaining empty space. The students agreed that the jar was now completely full.
The professor went on to explain that the jar represents everything that is in one's life. The rocks are equivalent to the most important stuff in life, such as spending time with your family and maintaining proper health. This means that if the pebbles and the sand were lost, the jar would still be full, and your life would still have meaning.
The pebbles represent the things in your life that matter, but that you could live without. The pebbles are certainly things that give your life meaning (such as your job, house, hobbies, and friendships), but they are not critical for you to have a meaningful life.
Finally, the sand represents the remaining filler things in your life. This could be small things such as social media or fake friends or other people’s opinions. These things don't mean much to your life as a whole, and focusing on them is likely only done to waste time.
The metaphor here is that if you start with putting sand into the jar, you will not have room for rocks or pebbles. This holds true with the things you let into your life. If you spend all of your time on the small and insignificant things, you will run out of room for the things that are actually important.