Sustainability on a team.
Great teams operate sustainably to maintain consistent results. Without sustainable operations, their efforts will become unmaintainable (by making tradeoffs that increase debt and decay), their processes will keep them from delivering, or their personnel will lose motivation or leave. Each of these affects their efficiency on different time horizons. Sustainability naturally declines without intervention: factors related to velocity are influenced by external factors, or factors unrelated at least to producing at the same standards levels. As such, much of what goes into merely maintaining the same level of sustainability requires the practice of continuous improvement.