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.

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.

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 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.

The typical 'buy and hold forever' strategy is riskier than perceived because the median lifespan of a public company is just a decade. This high corporate mortality rate, driven by M&A and failure, underscores the need for investors to regularly reassess holdings rather than assume longevity.

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.

The sign of a working diversification strategy is having something in your portfolio that you're unhappy with. Chasing winners by selling the laggard is a common mistake that leads to buying high and selling low. The discomfort of holding an underperformer is proof the strategy is functioning as intended, not that it's failing.

Historical analysis of investors like Ben Graham and Charlie Munger reveals a consistent pattern: significant, multi-year periods of lagging the market are not an anomaly but a necessary part of a successful long-term strategy. This reality demands structuring your firm and mindset for inevitable pain.

Even long-term winning funds will likely underperform their benchmarks in about half of all years. A Vanguard study of funds that beat the market over 15 years found 94% of them still underperformed in at least five of those years. This means selling based on a few years of poor returns is a flawed strategy.