Post-mortems of bad investments reveal the cause is never a calculation error but always a psychological bias or emotional trap. Sequoia catalogs ~40 of these, including failing to separate the emotional 'thrill of the chase' from the clinical, objective assessment required for sound decision-making.

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 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.

To decide whether to sell a long-held asset you're attached to, imagine it was sold overnight and the cash is in your account. The question then becomes: "Would you use that cash to buy it back today?" This reframe bypasses status quo bias and the endowment effect, making the correct decision immediately obvious.

Simply "thinking long-term" is not enough. A genuine long-term approach requires three aligned components: 1) a long-term perspective, 2) an investment structure (like an open-ended fund) that doesn't force short-term decisions, and 3) a clear understanding of what "long-term" means (10 years vs. 50 years).

To combat the emotional burden of binary sell-or-hold decisions, use the "Go Havsies" method. Instead of selling a full position, sell half. This simple algorithm diversifies potential outcomes—you benefit if it rises and are protected if it falls—which significantly reduces the psychological pain of regret from making the "wrong" choice.

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.

To combat the urge for constant activity, which often harms returns, investor Stig Brodersen intentionally reviews his portfolio's performance only once a year. This forces a long-term perspective and prevents emotional, short-sighted trading based on market fluctuations.

While having a disciplined rule like reviewing a stock after 24 months is useful, it should be subordinate to a more critical rule: sell immediately if the fundamental investment thesis breaks. This flexibility prevents holding onto a losing position simply to adhere to a predefined timeline.