The iron triangle illustrates the relationship between scope, cost and time.
The assumption is that these three interrelate in an adverse way with each other – that is, increasing one will increase the others. Quality suffers when all are fixed. But this ignores the fact that few value streams are effective. In fact, by focusing on principles of flow and lean we can deliver value in a shorter period of time, thereby reducing cost.
The essence of lean is to decrease waste by eliminating delays in the workflow. This requires reducing the need for:
Removing these delays not only shortens the time required to deliver value directly, but eliminates the work they create (see Why Looking at Delays In the Value Stream is so important). We can increase value without requiring additional work by focusing on those items that will deliver the greatest amount of value in the shortest amount of time. This is the definition of the Minimum Business Increment.
This combination of eliminating delays while focusing on the most important work provides a way to use the constraints of the iron triangle as a guide – not a limitation. We can get more value delivered in a shorter time and with less cost by attending to them.