The structural defenses — brand, network, cost, switching costs — that let a business keep earning outsized returns for decades instead of quarters.
Buffett's castle-and-moat idea, embraced fully by Munger: think of a great business as a castle, and of capitalism as an unending army of competitors trying to storm it. What keeps the castle standing isn't a low price today — it's a moat wide and deep enough that attackers can't cross it even decades from now.
High returns on capital attract imitators — rivals cut prices, copy products, or spend heavily to steal market share.
Brand loyalty, switching costs, network effects, or structural cost advantages make the attack unprofitable to sustain.
The business keeps earning above-average returns on capital, year after year, largely undisturbed by the attempted siege.
Global brand recognition and distribution reach built over more than a century let Coca-Cola command shelf space and consumer preference that a well-funded new entrant simply cannot buy its way into — long Berkshire's largest and longest-held equity position.
Munger and Buffett's favorite teaching example: a modest regional candy maker with such strong brand loyalty in its market that it could raise prices annually with almost no loss of volume, generating returns on capital far beyond what its small physical footprint would suggest.
A direct-to-consumer distribution model bypassing agent commissions gave GEICO a structural cost advantage over traditional insurers, letting it underprice competitors while remaining profitable — a moat built on operating model, not marketing.
Ask whether the advantage would still hold ten or twenty years from now, not just this quarter.
Check for real pricing power — can the business raise prices without meaningfully losing customers?
Look for sustained high returns on capital over many years, not a single strong cycle.
Stay alert to technological shifts that can erode even long-standing moats seemingly overnight.
Prefer moats that appear to be widening over time rather than merely holding steady.
Munger and Buffett would rather own a mediocre business protected by a strong moat than an excellent business with no defenses at all — because the moat, not this year's growth rate, is what determines whether the returns survive the next twenty years.