OneThing30: I’ll show you my mental model, if you show me yours

If it’s in your head, it’s a model

“Remember, always, that everything you know, and everything everyone knows, is only a model.”  Donella Meadows

What’s this got to do with sustainability?  Let me tell you a tale . . .

We share models all the time . . . when we talk about religion or politics or taxes or death.  We use words or diagrams or math or facial expressions or powerpoint presentations or – if you’re old like me – overhead transparencies.  We represent the real with something else that takes a bit less time or space.  I mean, how else could talk about the national economy except as an idea?  Even the data coming in from multiple sources is only particular data from particular places and at particular times; who really knows if it’s what we need to adequately “discuss the economic outlook of the United States.”

Even when I drive to work in the morning, I am working on a model from my head  (the actual streets, overpasses, stop signs, merges, ramps and parking lot at not in my head).  Ask two people you work or go to school with to draw a map that shows directions from home to school (or work).  Even if they lived next door to each other, you will undercover different mental models at work.

Expose your model to the light of day . . . 

This STOCK and FLOW map of the notorious chicken-egg story helps lay a few things bare.  (Another Donella note here – place your mental models in a place where people can see them, test them, challenge them.  It’s leads to clarity!)

We see two STOCKS – a clutch of eggs and a peep of chickens; that is, we can count them.  There are three FLOWSlaying, hatching, and expiring.  Each of these happen through time and at different rates; that is, if we stopped time (took a photo) we’d see the eggs and the chickens.  As for the flows, they’d go to zero (unless the photo actually captured a mid-flow occurrence); in a systems mental model, the flows go to zero and we can see the stocks.   Also, the size of the flows depends on the size of the stocks controlling them.

The Connector (blue directional arrow) shows an information connection – the number of chickens controls rate of laying; the number of eggs controls the hatching rate; and the number of chickens controls the rate of expiring.  In the connection from Chickens to Laying, the R refers to a reinforcing feedback loop:   the more chickens, the more laying of eggs; the more eggs, the more chickens; and so on.  In the connection from Chickens to Road Crossings to Expiring, the B refers to a balancing feedback loop: the more more chickens, the more road crossings, the more expiring, and, hence, the fewer chickens.

. . . to make the boundaries (aka, limitations) very clear.

This model shows some things, but clearly leaves some things out.  Can you see the assumptions in this model? (aside from its obvious cuteness . . . )

  • All eggs will hatch (that’s not likely)
  • All chickens will cross the road (also not likely – some will be content and stay put, others might by fricasseed or fried)
  • All road crossings will result in expiring  (variability in a species tells us there may be an agile chicken or two)

Of course, we might add those, but the model is less cute that way.

So . . . here’s a model that hits closer to home.

The more of us, the more we use . . . yo, duh!

World population really started to take off in the late 19th Century (check out the “SustainabilityThing” page).  Most demographers do not foresee that juggernaut slowing until the middle of the 21st Century.

STELLA diagram depicting two key STOCKS: Population and Resources . . . and these are locked in a feedback loop

To the left, the STOCK and FLOW diagram depicts a balancing feedback loop from Population to Using, but the Resource connected to death rate.  Not unlike the Chickens of Road Crossing fame.  Over time, the balancing loop helps equalize the system.

Taken together, the Stock/Flow Diagram and the graphical information (right) help us see, over the long haul, that such a relationship is unsustainable.

How can such an amped-up exponential system balance itself?  That’s a great question . . . and why all this new thinking needs to take hold as soon as humanly possible.


2 comments on “OneThing30: I’ll show you my mental model, if you show me yours

  1. Things sound like they might already be too late given current technology. The key variables seem to be the rate of technological progress and the extent to which we can collectively take advantage of these tools as a species in the face of massive, entrenched, and increasingly unaccountable power structures.



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