The Rule #1 Investing Checklist

Rule #1 investing, popularized by Phil Town, takes its name from Warren Buffett’s famous rule: never lose money. The practical way to follow it is a simple checklist applied to every stock — the 4M framework. If a business passes all four, and the price is right, you have a candidate.

1. Meaning

Do you actually understand this business and want to own it for the long term? If you can’t explain how it makes money in plain language, it’s outside your circle of competence — skip it. Conviction without understanding is speculation.

2. Moat

Does the company have a durable competitive advantage? Look for a wide, structural moat — network effects, brand, switching costs, cost advantage, or efficient scale — confirmed by consistent, high compounded growth in the Big Five numbers.

3. Management

Is leadership honest and capable, and do they allocate capital well? Check returns on invested capital (ROIC), debt discipline, and whether managers act like owners rather than empire-builders.

4. Margin of Safety

Is the price meaningfully below a conservative estimate of the company’s value? Estimate fair value with multiple methods and demand a discount, so you still win even if your assumptions are somewhat wrong.

The checklist in practice

Meaning, Moat, and Management tell you whether it’s a wonderful business. Margin of Safety tells you whether it’s a wonderful investment at today’s price. You need all four. Moatly runs this exact 4M checklist automatically for any ticker — scoring each M and calculating the fair value — so the discipline is built in.