Say you buy shares in a company. The price climbs and months later you sell for a healthy profit. Ask why it worked, and the answer is often some version of “I made a good call”. Now imagine the trade had lost money instead. Would you be as quick to blame your own judgment? Many of us wouldn’t. We may point to bad timing, a jittery market, anything but ourselves.

Psychologists call this “self-attribution bias”. Crediting ourselves for good outcomes, blaming something else for bad ones.

This bias matters more now that trading apps have made it easier for people with no formal training in finance to manage their own investments. Many of these apps offer tax-efficient accounts, such as stocks and shares Isas and self-invested personal pensions. They promote the tax advantages alongside low fees and sign-up incentives.

My colleagues and I explore this in our latest study, which examines self-attribution alongside two related biases – overconfidence and loss aversion – among people training to work in finance.

Behavioural finance exists as a subject because traditional theory, which assumes investors act rationally, struggles to explain why markets are prone to bubbles, or why we cling to losing positions long after we should sell. Self-attribution, overconfidence (an inflated sense of our ability relative to others) and loss aversion (feeling........

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