https://www.thetimedoctor.co.uk/big-rocks-and-time-management/

"The Big Rocks Story

A teacher is addressing their class, they fill a jug with big rocks and asks the class if it’s full. The class responds with a “Yes”. So, the teacher adds pebbles to the jug, and once again asks if the jug is full, and again the class responds, “Yes”. The teacher says “No” and now adds sand to the jug. In some versions of this story, it is taken a stage further by adding water to the jug.

My Explanation

The big rocks are the things in our life that are really important to us. The sand and the pebbles represent the small daily tasks we fill our lives with. If we don’t fit our big rocks in first, our lives will fill with only sand and pebbles, and there will be no room for the big rocks, BUT if we start with our big rocks, we create room for what’s important in life – and the sand and pebbles can only fill the spaces in between."