Prospect Theory
Why do losses tend to feel more significant than gains, even when they are the same size?
There are moments in markets where two outcomes can be objectively similar, yet experienced very differently. A gain of a certain size may feel modest or expected, while a loss of the same size can feel immediate and disproportionate. The difference is not in the numbers themselves, but in how they are perceived.
This is where Prospect Theory begins to provide a useful lens. It describes how people evaluate potential outcomes when faced with uncertainty, and how those evaluations differ from what traditional economic models would predict. Rather than treating gains and losses equally, individuals tend to assess them relative to a reference point, often placing greater weight on potential losses than equivalent gains.
The theory was developed by Daniel Kahneman and Amos Tversky in 1979, as an alternative to classical models of rational decision-making. Through a series of experiments, they observed that individuals do not simply maximise expected outcomes. Instead, choices are influenced by how those outcomes are framed, where they sit relative to a reference point, and how gains and losses are experienced psychologically.
One of the central insights of Prospect Theory is that losses tend to be felt more strongly than gains. This asymmetry helps explain why people may take risks to avoid losses, while being more cautious when securing gains. It also highlights the importance of framing. The same outcome, presented as a gain or a loss, can lead to different decisions.
In markets, this can be seen in the way positions are managed and risks are taken. Investors may hold onto losing positions longer than intended, hoping to avoid realising a loss, while taking profits earlier than planned to secure gains. Decisions become anchored to reference points, such as the original purchase price, and influenced by how outcomes are presented.
What makes this powerful is that it does not require extreme behaviour to take effect. Small shifts in perception can lead to consistent patterns over time. The theory does not suggest that people are irrational, but that their decision-making is shaped by how outcomes are experienced rather than how they are calculated.
You may recognise this in your own decisions when the possibility of a loss feels more significant than an equivalent gain, or when the way an outcome is described changes how it is perceived. There can also be a tendency to evaluate decisions relative to a specific reference point, even when that point may no longer be relevant.
Prospect Theory does not change the outcome.
But it helps explain why the same outcome can lead to very different decisions.