Even those who are only vaguely familiar with project management have likely heard of the three levers or triple constraint: scope, time, and cost. The theory goes that you can control any two of them, but the third will operate independently and uncontrollably. Demand the same scope in a shorter timeframe, and your cost is forced to escalate. Demand more work (scope) at less cost, and your timeline is going to stretch towards the horizon. While this is a neat conceptual tool and drives home the point that you cant have your cake, eat it, and then run away with the baker, the three levers are patently false. Heres why:
You really only have one lever
Once a project starts, cost and timeline are generally fixed. When major bumps are identified there may be a chance to reevaluate cost and timeline, but they rarely have the elasticity the three levers model implies. If your budgets and the completion date for a project changed on a daily basis, theres a high likelihood youd be hitting the unemployment line.
That leaves us with one lever: scope. Arguably scope is the most effective lever, since any adjustment to it usually results in changes to time and cost. Scope is also the most dangerous lever, since it can easily be changed without management knowledge or foresight. Most of us have been in meeting when a junior staffer, who must get approval on his or her pencil usage, gladly offers to do something without the realization that it might add tens of thousands of dollars and hours to a project. Even well-intentioned, seasoned veterans can glibly pile on scope without the project managers knowledge, effectively whittling away project funds just as seriously as if they threw a stack of bank notes out the window.
With this in mind, scope should be your most jealously guarded asset as project manager, and protected as if it were a stack of gold bars. Should a member of the team commit to scope increases, even unknowingly, gently explain the error and then get all parties together to agree to shelve the scope increase, or acknowledge the additional time and treasure required to make it happen, resources that may have to be taken from another element of the project since your time and budget are likely fixed.
The constraints of the triple constraint
The other fatal flaw of the three levers or triple constraint is that they assume infinite variability. Slide scope and time in one direction, and cost will slide in the appropriate direction infinitely. This is obviously not the case as some problems are more biased towards time-based or monetary solutions. Projects usually reach a wall where no matter how much money you throw at them, you simply cannot accelerate the project any further. Similarly, quality becomes an additional constraint that affects the other three levers. You can have all the money you want, but with an incredibly compressed timeline, quality will likely suffer.
While the three levers make for a nice conceptual tool and an excuse for a fancy graph in most project management text books, the concept is past its prime. Scope is the most effective driver of both time and cost, and usually the only variable a project manager can directly control without appeal to external parties for more time and money. Additionally, the three levers are themselves constrained by quality, and the fact that even near-infinite supplies of two of the levers will only push the third so far.
Patrick Gray is the founder and president of Prevoyance Group, and author of Breakthrough IT: Supercharging Organizational Value through Technology. Prevoyance Group provides strategy consulting services to Fortune 500 and 1000 companies. Patrick can be reached at firstname.lastname@example.org you can follow his blog at www.itbswatch.com.