The Four Constraints of Any Project

Posted by bob on September 26, 2013

In the first edition of The Dog Barks When the Phone Rings: An Engineer’s Guide to Solving Problems, I wrote that all projects are subject to three constraints: Time, Money, and Results.  The standard joke is that you can only control two.  Although every business represents a serious attempt to control all three constraints, experienced managers generally understand the limits of their control.  There is a figure below to help visualize the situation.


You can think of each constraint as a balloon filled with air, connected by hollow tubes to the other constraints.  As you squeeze one to control its size, one or both of the other balloons expand.

One day recently, I was staring at this figure and pondering the constraints we all face in various designs.  Suddenly a strange idea jumped into my thoughts and simply would not go away.  There are four primary constraints in every project, not three.  That makes the constraint triangle into a constraint pyramid—with triangular sides on each face.  What is this new constraint, you ask?  People.



I put People at the top of my constraint pyramid for a very specific reason.  I believe that this is the most important constraint among the otherwise equal limits.  Of course you can view the pyramid from any angle, so People might not be at the top of your pyramid—but I believe they should be there.

There might be some of you now saying, “Oh ‘people’ is just something you get by spending money, so you really don’t need a separate constraint there.”  I cannot accept that, and let me share why I believe that People are an independent and overwhelmingly important factor.

Is there any amount of money that would have induced Steve Jobs to leave Apple and go to work for Microsoft?  No, of course that would not have happened, even though there was a point in time when Steve Jobs had just been pushed out of Apple and Microsoft had plenty of money to offer.  Steve Jobs working at Microsoft just was never going to happen.

Likewise, there are many, many people out there looking for work (or not looking for work) that you would never hire to work on your project.  They might be perfectly suited for a given job, but they are not the right fit for your team.

This is why so many management texts make a big deal out of hiring and firing.  You must have the right people for your situation.

Having spent a lot of time studying this analogy and diagram, I realized that there is one more fairly subtle note that makes the concept work.  The balloon we call “results” should perhaps be called “bad results” and is really 1 divided by the value of Quality.  Mathematically, we can say:


This gives us some interesting consequences.  Bad Results can grow to a huge value as Quality approaches zero.  As Quality gets very, very big, the value of Bad Results approaches zero, but never quite gets there.  A wise Japanese manager once defined Quality as “anything that irritates the customer, other than price.”  I have often said that this definition is really saying the absence of quality is anything that irritates the customer, other than price, but today I think my reciprocal expression is really more appropriate.


Now our balloon and air-tube analogy really starts to work.  If we put the squeeze on money, our (bad) results swell up and maybe our schedule (time) starts to grow.  The same thing is true if we squeeze down on the Results (bad results) to get better quality in our project.  Squeezing bad results to get better quality might require additional time, money, or more (or different) people.

You can run through lots of different scenarios like this, all with similar outcomes.  If you squeeze on the People side, you often have fewer (or the wrong) people trying to accomplish the project.  Schedules can expand and more bad results (lower quality) will be the consequence.

There is an underlying assumption that is exposed by this discussion.  A given project with a defined set of goals will have a fixed “size” for its People-Time-Money-Results constraint system.  It is certainly true that large organizations will sometimes have additional capacity available to throw at a project.  This means they can endure rapid, short-term increases in People and Money without much impact.  However, most customers have limited flexibility in their project goals (schedule, price, quality) and therefore the pressure is ultimately applied to people to cure problems in the other constraints.

Yes, you are getting squeezed.