Work is decomposed into smaller units (stories) and retained, to create a sufficient level of healthy backlog for a team to deliver.  Poor/low backlog may result in a team being blocked by unidentified dependencies, stopping work to refine more backlog mid-sprint, or pulling in work that is not ready, just to keep moving forward.

Much like fueling up before a long trip, if you don’t have enough gas in the tank, get stuck in traffic or need to take a detour, you may find yourself stranded. Stopping for more gas often results in you reaching your destination later than originally thought.

How much backlog you’ll need will depend on the dependencies your team has, the complexity of your work, and the demands on your team to be predictable.