Trial and Error Is the Bedrock of Investing Knowledge

Warren Buffett's most expensive investment mistake cost him roughly $3.5 billion. In 1993, Berkshire Hathaway acquired Dexter Shoe Company for $433 million in Berkshire stock. The business deteriorated rapidly as low-cost imported shoes undercut its competitive position. Buffett later used the shares themselves — not cash — to make the acquisition, which meant the opportunity cost of those shares compounding at Berkshire's rate turned a $433 million deal into a $3.5 billion mistake by the time he wrote about it.

Buffett documented this mistake publicly and in detail in Berkshire's annual report. He assigned it a rough numerical cost. He articulated exactly what he got wrong — miscalculating the durability of the competitive advantage — and what principles the mistake reinforced.

That level of honest post-mortem analysis is not common. Most investors, professional and amateur alike, prefer to quietly move on from their errors. The losers get filed under "market conditions" or "bad luck." The winners get analysed thoroughly and attributed to skill. This asymmetry in how we process outcomes is one of the biggest barriers to developing genuine investing expertise.

The Problem With Long Feedback Loops

Investing is an unusually difficult skill to develop through experience, for a specific reason: the feedback loop is very long.

In chess, you know immediately if a move was tactically wrong — you lose the piece or the position. In surgery, the outcome is known within days. In most professions, the connection between decision and consequence is close enough in time that experience is a genuine teacher.

In investing, you might not know whether a decision was correct for three to five years. A stock you sold might recover and become a ten-bagger. A stock you held might take six years to finally produce returns you'd have earned more quickly elsewhere. A business whose "long-term prospects look excellent" might deliver those prospects over fifteen years, not three — which means your holding experience includes long periods of nothing happening.

This delayed feedback loop means that casual experience alone is nearly useless as a learning tool. The investor who makes fifty trades over ten years without carefully documenting their reasoning and outcomes is not necessarily a better investor in year ten than year one. They may simply be more confident — which, without genuine skill development, is more dangerous than helpful.

Deliberate Practice as the Accelerator

The way to develop skill in any complex domain with delayed feedback is through deliberate practice — not just repeated experience, but structured reflection that artificially shortens the feedback loop.

For investors, this means:

Document your reasoning at the time of every decision. Not just "I bought this because it looked good." The specific argument: this company has a durable competitive advantage because of X, the management has demonstrated Y quality through Z evidence, the valuation at the current price implies an annual return of approximately W over a five-year holding period.

Review outcomes against your original reasoning. When you sell a position, or when a significant positive or negative development occurs, go back to your original thesis. What did you expect to happen? What actually happened? Where was your reasoning correct? Where was it wrong?

Categorise your errors. Over time, patterns will emerge. Are you consistently over-estimating growth rates? Under-valuing the risk of management quality issues? Misjudging competitive dynamics in one particular industry? Each pattern you identify is an error type you can actively guard against going forward.

Charlie Munger built his famous mental-models checklist — which informed Mohnish Pabrai's own equally extensive checklist — partly from exactly this process: systematic documentation of failure modes, converted into active questions to ask before making future decisions.

Learning From Others' Mistakes

The deliberate practice approach has a significant shortcut available: the published records of investors who have gone before you.

Berkshire Hathaway's annual shareholder letters, written by Buffett from 1965 to the present, are probably the most valuable free investing education available anywhere. They include detailed descriptions of businesses Berkshire owns, honest discussion of mistakes, and clear articulation of the principles driving decisions. Reading them in order — chronologically, not just the most recent ones — is a master class in how investment thinking evolves through experience.

The Oaktree Capital memos by Howard Marks, available free at oaktreecapital.com, contain some of the most rigorous analysis of risk, cycles, and investor psychology published anywhere.

The Nomad Investment Partnership letters by Nick Sleep and Qais Zakaria, from 2001 to 2014, are available publicly and represent a detailed intellectual record of how two exceptional investors thought about businesses, mistakes, and the long game.

Reading these is not passive — it's a form of accelerated experience, borrowing the feedback from others' decades of decisions and incorporating the lessons into your own framework before you've had to pay for them personally.

The Right Relationship to Mistakes

The investor who learns fastest is not the one who makes the fewest mistakes. It is the one who extracts the most signal from every mistake they do make.

Mistakes are unavoidable in investing. Even the greatest investors of all time have made spectacular errors. The question is not how to avoid them entirely — it's how to ensure that when they happen, they teach you something specific that reduces the probability of the same error recurring.

This requires a relationship to mistakes that is honest without being self-punishing. The goal is not to feel bad about what went wrong. The goal is to understand it clearly enough to do something different next time.

Your investment journal is the most important tool for this. Every decision documented, every outcome reviewed, every lesson explicitly articulated. Over years, the journal becomes a personalised curriculum — the investing education that no course can replicate because it's built entirely from your own experience.

Learning investing through experience is unavoidable. Learning it efficiently through deliberate practice is a choice. It's one of the most rewarding choices you'll make.

The content on Gingernomics is for educational and informational purposes only and does not constitute financial advice. Always do your own research and consult a licensed financial advisor before making any investment decisions. Past performance is not indicative of future results.