Markets Are Not Rational Systems
Most investors begin with the assumption that markets behave in a broadly logical way.
Prices are expected to reflect available information. If new data emerges, prices adjust. If conditions change, markets respond. While there may be short-term noise, the underlying structure is assumed to be orderly, even if not perfectly efficient. And yet, over time, this expectation becomes harder to reconcile with experience.
Markets rise in the absence of clear justification and fall with a speed that seems disproportionate to the news. Narratives take hold, spread quickly, and then disappear just as abruptly. Assets become popular not because they are well understood, but because they are widely discussed. At some point, the question shifts from “What am I missing?” to something more fundamental. Are markets behaving logically at all?
What’s Really Going On?
The idea of rational markets is useful as a starting point. It provides a framework for thinking about how information should be processed and how prices might reflect underlying value. But it rests on assumptions that are difficult to sustain in real-world conditions.
Markets are not abstract systems operating in isolation. They are made up of participants, each with their own objectives, constraints, time horizons, and emotional responses. Information is not received uniformly. It is interpreted, filtered, and often reshaped before it influences decisions. In this environment, price is not simply a reflection of value. It is a reflection of behaviour, and that behaviour includes analysis and reasoning. But it also includes fear, confidence, imitation, and the influence of prevailing narratives. These elements interact in ways that are not always predictable and rarely balanced.
The Pattern Beneath the Surface
When viewed through this lens, certain patterns begin to make more sense. Markets tend to move in trends, not because value changes in a straight line, but because behaviour reinforces itself. As prices rise, confidence builds, attracting further participation. As prices fall, uncertainty increases, leading to caution or withdrawal.
Narratives play a central role in this process. They provide a way of explaining price movements after the fact and justifying participation in the present. Once established, they can persist even when the underlying conditions begin to change, and for that reason there is also a tendency for extremes to develop. Optimism can become overconfidence. Caution can become fear. In both cases, behaviour shifts in a way that pushes prices beyond what would be expected under purely rational assumptions. These patterns are not anomalies. They are recurring features of markets shaped by human participation.
Why This Matters in Markets
Understanding markets as behavioural systems changes how price movements are interpreted. It becomes easier to see why trends can persist longer than expected, and why reversals can occur without a clear external trigger. It also helps explain why attempts to time markets based purely on information often fall short. The information itself may be accurate, but its impact depends on how it is received and acted upon by others.
This perspective does not remove uncertainty. If anything, it highlights it. But it shifts the focus away from trying to predict precise outcomes and towards recognising the conditions under which certain behaviours are more likely to emerge. In doing so, it provides a more grounded way of navigating environments that are, by their nature, constantly evolving.
Where You Will See This in Yourself
This dynamic is not limited to the broader market. It shows up in individual decisions as well.
You may find your confidence increasing as prices move in your favour, even if your original reasoning has not changed. You may become more cautious after a series of losses, regardless of the opportunities in front of you. You may place greater weight on widely shared views, particularly when uncertainty is high.
There can also be a tendency to adopt the prevailing narrative, especially when it provides a clear explanation for what is happening. This can make decisions feel more grounded, even when they are being shaped by the same forces influencing everyone else. These responses are part of participating in a system where behaviour is interconnected.
Connection to the 12 Temptations
Many of the 12 Temptations emerge directly from this environment.
When markets are viewed as rational, deviations from a plan can feel like personal errors. When markets are understood as behavioural systems, those deviations become easier to recognise as responses to external pressures that are widely shared.
This does not remove responsibility for decision-making. It does, however, provide context. The 12 Temptations are not isolated weaknesses. They are natural responses within a system that constantly encourages them, and recognising this makes it easier to step back and observe what is happening, rather than simply reacting to them.
Markets do not need to be perfectly rational to function, but they do require participants to understand the difference between what should happen and what actually does.
This topic draws on a range of ideas including behavioural finance, narrative economics (Robert Shiller), reflexivity (George Soros), and the Adaptive Markets Hypothesis (Andrew Lo), all of which explore markets as evolving systems shaped by human behaviour.