- red and black show the elements of the feedback loop, and the interactions between them
- gray shows external causative factors, external to the loop.
cio' che segue e'
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In the figure
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The external causative factors are just causes, not effects.
In contrast, each element internal to the loop is both a cause and an effect.
Because this is a positive feedback loop, once it gets going it keeps going, even if you remove all of the external causes. At this point, examining the loop will not tell you what the original external cause(s) might have been. The present situation is controlled by internal causes, internal to the loop.
What’s worse, at this level of detail is irreversible. The figure does not show any way to unlatch the feedback loop, once it gets latched up. One hopes that there are other factors, not shown in the diagram, that will allow the real-life situation to be unlocked.
From a policy and planning point of view, you would very much like to know what the original causative factors were, so you can take action to prevent similar feedback loops from starting up in the future. However, you can’t figure that out by looking at the present state of this loop. Furthermore, knowing the original cause(s) doesn’t necessarily tell you how to change the state of this loop as it stands.
Also in figure are symptoms, shown in light blue. These are external effects. They are not causes, and not part of the feedback loop.
Applying some intervention to scrub away the symptom does not change the cause-and-effect relationships within the loop. For example, suppose you find some observable quantity that is initially a 100% reliable symptom, initially 100% correlated with some problem you care about. If you scrub away the symptom, it does not cure the problem. All it does is break the correlation, making the quantity no longer a reliable symptom.
Other feedback loops are very common in technology; for example, the thermostat on a household heating/cooling system is part of a feedback loop. There are also feedback loops involved in climate change, including some negative feedback paths along with some very scary positive feedback paths.
ref: http://www.av8n.com/physics/causation.htm