Ben Snyder has several posts on PM Hut about the demise of the "Iron Triangle" in PMBOK® Version. For some reason PMI decided to remove this concept, just when those of us in the defense and space business are starting to use the phrase "Ponzi Scheme."
Just as a reminder, the three invariant variables in any project are, Cost, Schedule, and Technical Performance. Technical Performance includes the quality measures from the previous version of PMBOK®. Technical Performance Measures describe the behavior of the product or service in units meaningful to the buyer.
The relationship between these three variables is coupled, in likely non-linear ways, but they are coupled and this coupling is inseparable. There have been those that suggest this coupling can be broken. It can't.
Just so we don't forget - since PMI removed the reminder - making trades between Cost, Schedule, and Technical Performance and NOT expecting unfavorable impacts is a Ponzi Scheme. Treat anyone suggesting those trades can be made with no impact in the same way you'd treat Charles. Run Away.
