Peter Lynch wrote in One Up On Wall Street: 'Go for a business that any idiot can run — because sooner or later, any idiot probably will.' The line captures something more important than its irreverent tone: industry structure determines what's possible at the ceiling, and even modest management can produce decent results in a structurally good industry, while exceptional management can struggle to outrun a structurally bad one. Industry analysis is therefore the prerequisite for company analysis — and the framework integrates Porter's Five Forces (lesson 2), moats (lesson 1), and TAM expansion (lesson 4) into a single view of the pond you're fishing in.

Cyclical sectors include Energy, Materials, Industrials, Consumer Discretionary, and Financials. Their revenue and profits expand and contract with GDP growth, capacity utilization, and consumer confidence. Defensive sectors include Utilities, Healthcare, and Consumer Staples.

Their demand stays relatively stable regardless of cycle (people keep using electricity, taking medicine, buying groceries).