What Is a Moat — and How Wide?

"If you're a long-term investor, you can take advantage of the volatility of others." — Joel Greenblatt

A moat is a sustainable competitive advantage — the thing that stops rivals from competing away a company's high returns. Without one, strong profitability simply attracts competition, and returns drift back towards average.

There are five main sources of a moat:

• Network effects — each new user makes the product more valuable to the others (for example, payment networks and social platforms).
• Switching costs — leaving is painful or expensive (enterprise software).
• Cost advantages — structurally lower costs than rivals (large-scale retail and cloud infrastructure).
• Intangible assets — brands, patents and licences (luxury goods, premium consumer brands).
• Efficient scale — a market only big enough to support one or two players profitably (railways, waste management).

The investor's job is not just to spot a moat but to judge how wide and how durable it is. A narrow moat narrows further; a wide one can protect high returns for many years.

Illustrative example: a payment network

A business built on network effects and switching costs can sustain high returns on capital for a long time, because no rival can easily replicate the network or persuade everyone to switch at once. That durability — not any single year's profit — is what the moat protects.