Stocks don’t move alone. A bank tends to rise and fall with other banks; a carmaker with other carmakers. Grouping companies by what they do — into sectors — explains a lot of why prices move together, and helps you avoid accidentally betting everything on one thing.
Sectors: companies that rhyme
The market is sliced into broad sectors — technology, financials, healthcare, energy, consumer goods, utilities, and more. Companies in the same sector share customers, costs, and risks, so news that hits one often hits all (an oil-price spike lifts energy and squeezes airlines at once).
Cyclical vs defensive
The most useful split is how a sector behaves with the economy:
- Cyclical sectors — carmakers, travel, luxury, banks — boom when times are good and slump when wallets tighten. Their earnings swing with confidence and spending.
- Defensive sectors — utilities, consumer staples, healthcare — sell things people buy in any economy (electricity, food, medicine). Their earnings, and prices, hold up better in downturns.
The business cycle
Economies move in a rough business cycle: expansion → peak → contraction → recovery. Different sectors tend to lead at different stages — cyclicals early in a recovery, defensives as growth fades. Nobody times this perfectly, and you don’t need to. The lesson is gentler: don’t unknowingly load up on one type.
Why it matters: diversification
This is the diversification idea made concrete. Spreading across sectors — and between cyclical and defensive — smooths the ride, because they don’t all fall together. A portfolio that’s all cyclicals is a single bet on the economy in disguise.
The takeaway
Stocks cluster into sectors that move together; cyclical ones swing with the economy while defensive ones steady the ship. Spreading across them is real diversification — protection against any single shock. (This is education, not investment advice.)