How Buffett evolved as an investor (1966-76 letters)

Buffett's early years at Berkshire Hathaway read like a slow-burning pivot. What began as a struggling textile business gradually became the foundation of a capital-compounding empire. But that transformation didn't happen overnight and certainly not by accident.

In this instalment of our series on Warren Buffett's shareholder letters, we revisit the decade between 1966 and 1976—a stretch where the seeds of his modern-day investing philosophy were quietly planted. The letters from this period are not flashy. They don't feature billion-dollar acquisitions or market predictions. Instead, they are rich with something more valuable: clarity.

Let's walk through a few core ideas that shaped this formative decade.

The capital trap of a dying business (1966)

The 1966 letter captures the brutal reality of running a capital-intensive business in a fast-moving world. Textiles, Buffett admitted, were a minefield of obsolescence. Machines you bought today could be outdated tomorrow, not by innovation, but by necessity. "The textile machinery industry," he wrote, "is constantly striving to render [our assets] obsolete."

With $24.4 million sunk into plant and equipment (but only $6.3 million after depreciation), Berkshire was not sitting on assets, it was sitting on liabilities that aged faster than the returns they generated.

Buffett's insight here is profound: capital expenditure in such a business is not discretionary; it is survival-driven. And when survival requires constant reinvestment with low returns, the business is a treadmill, not a moat.

That is why Buffett pivoted. He did not abandon the business, but he began channelling capital elsewhere—with a clear-eyed recognition that marketable equities, not looms and spindles, might offer a better return on effort.

His decision to invest surplus funds in common stocks was not just about yield. It was about flexibility. "This provides us with the opportunity to participate in earnings derived outside of our textile business," he said. Translation: our capital deserves better than to be trapped in a business that can't compound it.

Insurance: Growth, but only with discipline (1972)

By 1972, Buffett was deeply immersed in the insurance business. But he was not drinking the Kool-Aid of growth for growth's sake.

In this year's letter, he made a simple but powerful statement: underwriting profitability is the only real measure of success. Not premium growth. Not market share. Not scale.

This is classic Buffett—you get lessons in discipline masquerading as operational updates. Insurance is seductive because it brings float: money you can invest before it technically belongs to someone else. But if you underwrite poorly, that float becomes a ticking time bomb.

So, Buffett's rule was firm: grow only when you are doing it right. And doing it right meant writing policies that made money before investment income. No amount of asset returns could justify stupid underwriting.

There is a quiet metaphor here, too. Just like he refused to reinvest endlessly in dying textile machines, he refused to write unprofitable policies just to look busy. Capital, to Buffett, should be treated like family silver, not poker chips.

A business owner's checklist for stocks (1975-76)

By the mid-70s, Buffett's philosophy of stock investing had matured into something timeless. In the 1975 and 1976 letters, he laid out the criteria he uses to buy businesses. It was not about momentum. It was not about forecasts. It was about business fundamentals—four of them to be specific:

• Favourable long-term economics
  
• Competent and honest management
  
• A purchase price that makes sense for a private owner
  
• Familiarity with the industry and its long-term traits

This list may seem obvious today, but it was contrarian in an era obsessed with charts, trends, and quarterly earnings. Buffett was not trying to outguess the market. He was trying to think like a business owner.

And with this mindset, market fluctuations became background noise. As he put it: "stock market fluctuations are of little importance to us, except as they may provide buying opportunities." Business performance, on the other hand, was everything. He was not looking for action. He was looking for compounding.

Conclusion

Between 1966 and 1976, Buffett did not just change direction; he changed altitude. He moved from managing businesses that consumed capital to acquiring businesses that created it. From textile machines to underwriting discipline to owner-like investing, he built a worldview rooted in prudence, permanence, and performance.

It was in these quiet years, not the headline-grabbing ones, that Buffett sharpened the tools he still uses today: a deep respect for capital, an allergy to mediocrity, and the humility to wait for the right pitch.

This was not reinvention. It was evolution. And it laid the tracks for what Berkshire Hathaway would eventually become.

Also read: Buffett's 1984 letter: A guide to capital allocation & more

This article was originally published on August 13, 2024, and last updated on April 03, 2025.