Thad Scheer
SPHERE OF INFLUENCE, INC. – software studios and services
The iron triangle myth
There are several myths that surround Agile Software Development – but I see this one frequently. It's the notion that by some magical means Agile Software Development makes the iron triangle obsolete.
For anyone not familiar with it, the three sides of the iron triangle are Cost, Quality, and Scope. Project leadership can control at most two of the sides. For example, a project might need to meet Cost and Quality targets – that means it needs flexibility to adjust Scope (e.g. you might need to remove features in order to meet the other two targets).
When people describe Agile to newbies the impression is often given that the iron triangle problem is solved because Agile uses fixed delivery schedules, intense emphasis on quality, and customer intimacy to deliver desired functionality. That is enough to confuse people into thinking Agile allows a project to control all three sides of the triangle. Of course, the iron triangle does not bend – not even for Agile projects. If cost and schedule are fixed, a project will still need flexibility to adjust scope (i.e. the customer might not get exactly what they want).
Agile uses intense prioritization to offset this. On cost limited projects the customer gets the most desired features from the set of features they can afford. Similarly, on schedule limited projects the customer gets the most desired features from the set of features the team can deliver in the allotted time.
When it comes to quality, Agile teams prefer to set the quality line pretty high as a default. This comes out of the XP influence. This doesn’t mean you can’t crank up the quality to some insane level – say for aviation, medicine, or whatnot, but at least it won’t fall below a minimum “ethical” threshold. This high discipline, however, has costs and will remove some freedom on the other two sides of the triangle.
The bottom line is that Agile does not magically break the iron triangle. Project management is still project management, and product development is still product development. Agile doesn’t turn either on end.