A major red flag for catastrophic losses is "thesis creep": repeatedly changing your reason for owning a stock as it declines. An investment made because it's a 'good business' at $10 becomes a 'value play' at $8, then a 'liquidation play' at $3. This intellectual dishonesty prevents cutting losses when the original thesis is broken.

Regularly re-evaluate your investment theses. Stubbornly holding onto an initial belief despite new, contradictory information can lead to significant losses. This framework encourages adaptation by forcing you to re-earn your conviction at regular intervals, preventing belief calcification.

An investment thesis is a plot. The theatre rule of "Chekhov's Gun"—that a gun shown in Act 1 must fire by Act 3—is a powerful mental model. If a key catalyst for your investment doesn't materialize within your expected timeframe, the story has fundamentally changed, signaling that it may be time to exit.

To avoid emotional, performance-chasing mistakes, write down your selling criteria in advance and intentionally exclude recent performance from the list. This forces a focus on more rational reasons, such as a broken investment thesis, manager changes, excessive fees, or shifting personal goals, thereby preventing reactionary decisions based on market noise.

The speaker proposes a three-year rule: if a stock investment hasn't appreciated in three years, it's time to question your own analysis rather than blaming the market. This mental model forces a re-underwriting of the investment thesis and prevents holding onto losing positions indefinitely.

Instead of making emotional decisions, establish "kill criteria" for each investment: a specific KPI (a state) that must be met by a certain time (a date). If the company fails to meet the predefined metric, you sell. This provides a disciplined, objective framework for portfolio management.

Contrary to the 'hold forever' value investing trope, a three-year period of underperformance is a strong signal that your initial thesis was flawed. It's better to admit the mistake and reallocate capital than to stubbornly wait for the market to agree with you.

True investment maturity isn't about holding through drawdowns. It's about recognizing when new information invalidates your thesis and selling immediately. The common instinct to defend a position by buying more is a costly mistake that turns event-driven plays into distressed holdings.

According to investor Howard Marks, people sell assets either because they're up (to lock in gains) or down (out of panic). Both are poor reasons. The only valid reasons to sell are if your original investment thesis is no longer true, or if you've found a demonstrably better opportunity.