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.

Combat indecision and emotional attachment by pre-committing to sell an investment if it fails to meet a specific metric (the state) by a specific deadline (the date). This creates a pre-commitment contract that closes long feedback loops and prevents complacency with underperforming assets.

Durable Capital's process includes a mandatory three-year look-back for every investment, comparing the original thesis to reality. This is crucial because while small deviations can be excused quarterly, compounding them over 12 quarters reveals significant thesis drift. The formal review forces an intellectually honest assessment of whether a slow-moving problem has become critical.

The rule for selling a stagnant stock after three years is less relevant for 'wonderful businesses' that constantly create value. Even if the stock price is flat, the underlying value has grown, improving the risk/reward. The rule is more critical for static-value investments where timing is everything.

The modern market is driven by short-term incentives, with hedge funds and pod shops trading based on quarterly estimates. This creates volatility and mispricing. An investor who can withstand short-term underperformance and maintain a multi-year view can exploit these structural inefficiencies.

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.