When President Trump announced Sunday that a memorandum of understanding with Iran was "largely negotiated," global equity markets moved quickly. The TSX rose more than 1% Monday on hopes that the Strait of Hormuz would reopen, energy inflation would ease, and the worst of the geopolitical risk premium would begin to fade. It was, by every measure, a relief rally.
Relief rallies feel good. They also, reliably, produce one of the most expensive mistakes in retail investing.
What the Disposition Effect Predicts for This Moment
The disposition effect, first named by Hersh Shefrin and Meir Statman in their 1985 paper "The Disposition to Sell Winners Too Early and Ride Losers Too Long," describes a consistent pattern: investors sell positions that have appreciated and hold positions that have declined, regardless of whether selling or holding is the correct decision. The psychological architecture underneath this is dual: loss aversion, which makes realizing a loss feel disproportionately painful, and the certainty effect, which makes a guaranteed gain feel more attractive than a potentially larger uncertain gain.
Terry Odean's 1998 study of 10,000 brokerage accounts confirmed the pattern empirically. Investors in his sample realized gains at a rate roughly 50% higher than they realized losses. Losing positions were held an average of 124 days; winning positions were held 104 days. The consequence was direct and measurable: the sold winners outperformed the held losers by an average of 3.4 percentage points over the subsequent year.
This is the trade that will happen across thousands of Canadian retail portfolios in the next several days, triggered not by analysis but by the emotional signal of relief.
The Asymmetric Portfolio the Iran MOU Has Created
Monday's TSX session illustrated exactly the landscape the disposition effect thrives in. The S&P/TSX Capped Energy Index fell 3.38% as crude oil dropped on Hormuz reopening optimism, erasing months of war-premium gains from names like Canadian Natural Resources, Suncor, and Cenovus. Meanwhile, the TSX Capped Financial Index rose 0.90%, with RBC, TD, and BMO each advancing roughly 1% heading into a critical earnings week. Gold miners surged: Agnico Eagle gained 4.6%, Barrick 4.2%, Wheaton Precious Metals 5.6%, as gold held above USD $4,500/oz despite some peace-premium selling.
The result is a portfolio split between positions that look like clear wins -- financials, gold miners -- and positions that look like losses reversing from recent highs: energy names down sharply on the week. The disposition effect's prediction is precise: investors will sell the financials and the gold miners that have appreciated, and hold the energy names that have declined, waiting for recovery that may not arrive on the timeline they imagine.
The energy sector's 41.8% indexed gain from the March 3 pre-closure baseline peaked at the week of May 12 before reversing sharply on Hormuz deal optimism; the TSX Capped Financial Index gained a steady 5.8% over the same period with no war-premium component.
The chart above shows how sharply the two sector series have diverged since the week of March 3. That divergence is the asymmetric portfolio the disposition effect operates on this week.
Why Loss Aversion Makes Energy the Hardest Position to Evaluate Clearly
Kahneman and Tversky's prospect theory, developed in 1979, established that losses feel approximately twice as painful as equivalent gains feel pleasurable. For a client who accumulated Canadian Natural Resources or Suncor during the war premium -- positions that have fallen 3% on Monday alone and more than 10% over the past week -- the emotional weight is significant. The reference point matters enormously: a client who bought at $45 and watched the position rise to $55 before this week's decline to $48 does not experience an $8 gain. They experience a $7 loss from their peak reference point.
This is the psychological architecture that produces holding when selling would be rational. The client is not irrational. They are responding to a deeply human cognitive system that was not designed for financial markets.
The Advisory Opportunity in a Relief Rally
The disposition effect is most powerful when it operates unexamined. The advisor who names it -- who calls a client this week and says "here is what this kind of moment typically does to portfolio behaviour, and here is why it is worth thinking carefully before you act" -- is providing something that has a direct, measurable dollar value. The research is not ambiguous about this. Odean's 3.4 percentage point annual cost of the disposition effect, applied to a $500,000 portfolio, is a $17,000 annual drag. Framed that way, the advisory conversation is not a soft behavioural intervention. It is a return on advice.