Know Your Scarcity

Fred Brooks, the computer scientist who 35 years ago wrote the still-relevant The Mythical Man-Month, has written a new book, The Design of Design, and Kevin Kelly interviews him in Wired. It’s interesting throughout, but the following struck me as particularly insightful:

The critical thing about the design process is to identify your scarcest resource. Despite what you may think, that very often is not money. For example, in a NASA moon shot, money is abundant but lightness is scarce; every ounce of weight requires tons of material below. On the design of a beach vacation home, the limitation may be your ocean-front footage. You have to make sure your whole team understands what scarce resource you’re optimizing.

I believe Brooks’s point about money often not being the scarcest resource is spot-on; as Stella Adler used to say, “your talent is in your choice.”

Ian Kemmish

I'd say that The MMM is a) scarcely known at all, and b) revered by those who do know it.

But I think that snippet may be oversimplifying. Money may not be scarce in a politicking-up-the-wall contest like a moonshot, but if the cost of shaving 5Kg off the weight of your lander outweighs the cost of the fuel needed to get that 5Kg to the moon, then it's still money that calls the shots. If it doesn't, it;s the weight that calls the shots. Or maybe it doesn't, but the time taken for the redesign means you get to the moon second. Which is scarcest, money, lightness, or time, can change from moment to moment in a complex dance. (Something I'm sure Mr Brooks understands thoroughly!)

Let's just hope this book doesn't lead to a glut of pointy-haired bosses deciding that the first thing they need to do in their project is to decide what's scarce and set that decision in stone for all time....



whats up with the lack of wolfers? I miss his post

Eric M. Jones

Moon Landing Economics: I think you have it slightly wrong. It's the safety of the human cargo that called the shots. Everything is subservient to safely landing and returning the human cargo.


Were that so, Eric M Jones, we'd never have gone in the first place...

I really liked this when I read it in Wired and it's just as impactful reading it again today. Thanks for it.


In Ian McHarg's layer cake for designing with nature, one was supposed to be determining what where the 'knock-out constraints' on the design... Sort of the negative side of 'know your scarcity' concept..

R.M. 'Auros' Harman

I disagree with the idea that most projects have a single binding constraint that renders the others irrelevant. It's much more likely that optimizing against any one constraint will pessimize several others.

Devinder K.Sharma

Brooks's comment on the criticality of various inputs in the design process is right on target. Finding out the scarcest resource in the process is like knowing one's constraints in advance. It definitely leads to better appreciation of the problem being tackled and optimising the output to suit the caller's demand. Money certainly is no longer the scarcest resource today, as Dubner says.

Eric M. Jones

@6- R.M. 'Auros' Harman

I agree with you (but you mean refudiate, not pessimize, you betcha...).

In my earlier post, I was too quick to pooh-pooh the notion that weight is the limiting resource (or so). What I should have said was that weight (actually mass) is only one of several variables that are important to consider.

Like most things in life there are tradeoffs. If one had had more thrust or money or time (or Russian propulsion engineers); then mass would have been less important.

It is tautological that everything should be as light as it can be for a particular application, but no lighter. Everything should be as simple as it can be but no simpler....

But my main disagreement is simply that Fred Brooks paints a simpler picture than can be supported by the task of real engineering. Of course I didn't read his book, but I read the MMM and that's why I won't read it.


In a particular optimizing situation money may not be the scarce resource, but from a general economic perspective money can always buy more of whatever is scarce.
Extreme cases (like space travel etc) are ... extreme cases.

This seems to be more a managerial point than an economic point.

Young Lee

Fascinating perspective. Applied to healthcare reform, it is the ethics that is scarce - doctors and hospitals charging too much; insurance companies denying weak people. In case of financial reform, again it is ethics that is scarce - bankers and traders earning too much money.
Adam Smith assumed plenty of ethics when he proposed market economy. Now that we know ethics is a scarce commodity, we should redesign healthcare and financial systems from this scarcity perspective.

Walt French

@Auros Harman: take a simple assumption - that marginal costs are rising in the relevant zone, e.g., that to increase production you need to pay more for a lower quality employee than the ones you hired earlier - and then the optimum point, assuming good divisibility, is where each cost tradeoff is equal.

A more restricted example, easier to grok if harder to generalize: there's no sense building one tunnel 40 feet wide if all the others for a train route are only 25 feet wide. Each bottleneck should be a similar constraint.

This is design as practiced by, say, Apple. To the best of their ability, just enough "headroom" over the capabilities required, in each of several ways, so that as your needs/usage expand, you haven't paid for 4X the memory that you need while your CPU is maxed out. I'm sure others do similarly.

Frost Knight

It sounds very similar to Goldratt's Theory of Constraints. Design around your bottlenecks (or scarce resources).


On the other hand, Mr Brooks also observes that frequent failure of the rational design process "is due to the desire to enter into binding contracts with specified requirements much too soon."

Juan Camilo Esguerra

Hmm....esxcessive weight means you need more fuel, and fuel is expensive so you need more money... I think at the end is always money. You think the problem is the lack of talent in your company you can hire someone more qualified but it will cost you more money (money again) and the beach house problem... you want more ocean front footage, guess what, money, more money to buy a little more... so the scarce resource always becomes money.

Eric M. Jones

@14- Juan Camilo Esguerra


I was priviledged to attend a seminar run by one of the top NASA project engineers during the 1960's. I discussed with him my own problem that once our design work commenced, management was inclined to "add features". while not allowing a revision of the schedule. While I was smart enough to try to add time for these unspecified and unknown features that I knew would be added-- beforehand, this was not permitted. This was a formula for stress, and schedule problems, and over-budgets.

His answer was, "I just say fine...then I just tell them to bring money and lots of it, otherwise I won't talk to them".

Money is the only limiting resource in building or designing anything. Money plays the same part in making stuff as energy does in physics.


If money is not scarce, why do not just hire three teams instead of one and let them compete.


It might be better to think of money as merely the proxy for whatever resource you're missing, and even this starts to show that money, in of itself, is not the actual limiting factor. I can buy more fuel to send the man into space, but I can't endlessly expand it to the point that I'm converting the land mass of Cape Canaveral into a fuel depot. I can buy more ocean-front property for my beach house, but I can't buy all of California. And typical of the person who wrote the Mythic Man Month, just because I can throw more programmers at a project that's late doesn't mean I make the deadline.

In theory I can do all those things with enough money. In reality, there are things money can't buy, or there comes a break point where costs so far exceed returns that continuing would be insane. After all, if we had unlimited resources, there would be no need of economics; this is the study of how to work with *limited* resources.



I've been a software developer for 25 years. I read MMM years ago. I should probably look over it again.

In my experience, two of the scarest resources are:
+ Clear requirements
+ Time to do the coding

A HUGE amount of time is spent in just trying to figure out what the customer wants and what it should do.

Eric M. Jones

@16- vincent. "If money is not scarce, why do not just hire three teams instead of one and let them compete."

Why not just hire competent Chinese and Indian management teams for 1/3 the money?

@17- Kenneth "In reality, there are things money can't buy, or there comes a break point where costs so far exceed returns that continuing would be insane..."

Oh? Ever see Boston's Big Dig? Endless money spent. No sane solution in sight.


You people saying 'at the end of the day the constraint is always money' - money is as we know an abstract thing, and you're putting all the constraints into the money bucket, which I suppose isn't TOTALLY wrong, but it doesn't shed any light on how to attack a problem (once you've secured funding).

It's not true that 'with enough money, you can do anything' - Brooks is just saying your efforts with the moon shot are better spent cutting down weight than pumping infinite money into rocket fuel. Just find the area where your improvements will have the most benefit, and then handle other constraints when they become too...'pessimized'...