There is a well-known story about how to “properly” fill a jar with sand, rocks, and water. For the detailed story, please refer to the video below. The story is often used as an analogy to inspire people about the importance of priority.
But from the operations management perspective, the story also tells us an important principle about the capacity utilization. The fact that it still had space to fill sand and water after the rocks are filled first, is because the irregular shape (variation) of the rocks were inhibiting the space from being utilized efficiently!
Efforts to reduce variations can be seen everywhere! Workstations in the factory is moving in “cycle times”, packages follow certain design specifications so that the container (or truck) spaces can be maximally utilized.