Every important decision involves a degree of uncertainty. Changing jobs, starting a business, moving to another city, beginning a relationship, choosing a course of study, or investing in a project always means confronting a future we do not know.
How do we keep making decisions of this kind? We might say that we estimate the probability of success. We assess risks, opportunities and obstacles, and then decide whether or not to proceed. This picture has a logic of its own, but it only partly describes what actually happens in the mind.
In most situations, we do not have the information needed to arrive at a reliable estimate of probability. We do not really know the probability of building a successful business, writing an important book, changing careers or building a lasting relationship. There are too many variables, and many of them are unknown or even unknowable.
Despite this, some possibilities seem realistic to us and others impossible. Herbert Simon showed how human beings make decisions under conditions of bounded rationality, that is, with incomplete information and finite cognitive capacities. The perception of uncertainty therefore seems to depend on something other than the mere calculation of probabilities, whether formal or spontaneous.
One possible interpretation is that human beings perceive uncertainty by assessing how navigable the mental paths linking the present to a given outcome are.
When we imagine the future, we see a sequence of steps. If I want to change jobs, I imagine a search, a contact, an application, an interview, then a selection process and finally a new contract. If I think of opening a restaurant, I imagine premises, customers, suppliers and an opening. If I think of writing a book, I imagine chapters, revisions and much else before publication.
The mind is constantly constructing paths.
This mechanism is so natural as to be almost invisible. When we reflect on a goal, we rarely picture all the variables involved. Instead, we construct a succession of stages linking the present to the desired future, and the sense of feasibility seems to depend above all on the quality of these paths.
Our sense of probability may derive, at least in part, from the ease with which the mind can construct a plausible sequence of steps between a present situation and a future one. When we can imagine a route leading to the outcome, confidence grows. When we cannot construct any path at all, uncertainty increases.
This explains why some seemingly unlikely undertakings are nevertheless attempted. Those who take them on have a story that links the present to a possible future.
Amos Tversky and Daniel Kahneman observed something similar through the so-called simulation heuristic. Events we can easily imagine tend to seem more plausible to us. The ease with which we construct a mental simulation is often interpreted as a sign of the probability of success.
Human beings deal with uncertainty by constructing compressed representations of the paths linking the present to possible futures, rather than modelling the full complexity of the situation.
We might hypothesise that the mind uses paths because they offer an economical solution to a larger problem. The world is too complex to be processed in its entirety. The information available almost always exceeds our capacity to process it. Working memory, like attention or the number of variables we can keep active at the same time, is limited.
Representing a goal as a chain of steps thus becomes a way of representing complexity in compressed form. Telling the story and imagining the steps take the place of the impossible alternative of modelling the entire system.