Rule of Lost for the entire System:

An Hour Lost at Bottleneck is an Hour Lost for the entire System

Let us presume that there is adequate demand for parts in the market. Now, if the bottleneck of the previous instance (in Rule 3), is running at 100% capacity and, accidentally, it stops for an hour, say, for repair & maintenance. An hour lost on this bottleneck shall reduce directly the overall production rate (throughput) by one hour. This shall be the case, even if there is sufficient inventory pile-up before the bottleneck. An hour lost on bottleneck may never be recovered because this machine shall never have time' to process parts, which would or else been made in the lost time. This is because of non-availability of buffer capacity for bottleneck. Hence, an hour lost on bottleneck is an hour lost for the entire factory. In brief, if the bottleneck has lost one hour, the total impact is : "the factory has been stopped for one hour".