Scope, Schedule, Cost – they are classics, but do they remain useful?. I’ve heard many practitioners call the Triple Constraints (TC) obsolete or, at least, inadequate.
Many PMs point out that we need to factor in quality. I don’t have a problem with this one. On the other hand, I didn’t know that Scope didn’t include quality. For me, Scope never meant just a list of things or features. Without a set of acceptance/quality criteria, Scope would be too fuzzy. So, with that proviso, I think Scope is still a good one.
What about Cost? I’ve had a lot of PMs tell me with an honest expression that they don’t think about costs because “they have to do it with what they have so it’s all fixed cost and so it doesn’t matter anyway.” Whoa. Maybe some of us forget that cost is really a measure of resources. For a lot of my projects, we were more focused on the hours/days of resources needed than on the $$. Even in a “fixed cost” environment, we will compete for resources – especially critical (in the sense of scarce) resources. If you don’t usually deal with the $ costs, let’s use Resources as the constraint. So, I think Resources is OK.
No one seems to question the importance of Schedule – except to say that the Schedule is always too short. Of course, if it is always too short, what does that say about either our estimation skills, or our assumptions about reality… but that’s for another time.
Another question is “Where’re the risks?” Clearly, risks are a critical consideration. For example, we may have a TC with a 10 month schedule. Examining risks, we find that we have a very low risk of missing the TC, but we have a significant risk being “left behind” a competitor with a significantly improved product coming in 6 months. If we want to reduce the competitive risks, we will have to rebalance the TC – perhaps by accepting a smaller Scope, or increasing Resources. in order to reduce the Schedule. So, maybe we have this:
So, I’m still a fan of the Triple Constraints. Except now it’s the Quadruple Tetrahedron? I think Triple Constraints + Risk might be better.