“Sustaining continuous flow also serves to surface any problem that would inhibit that flow. In essence, the creation of flow forces the correction of problems, resulting in reduced waste. We often use the analogy of a ship on a sea filled with dangerous rocks. As long as the rocks, like problems, are covered with water, like inventory, it’s smooth sailing. [Toyota leader Taichi] Ohno discovered that if he reduced the inventory, the problems surfaced, and people were forced to solve them or the system was forced to stop producing. This was a good thing, as long as the damage was not too severe and the people had the capability to improve the process so that the problems did not recur. He also learned that the system needed some minimal level of stability, or the reduction of inventory would just result in a loss of production…” 

The Toyota Way Fieldbook by Jeffrey Liker & David Meier (McGraw-Hill, 2006) p. 81.