Costco Wholesale Corp.'s 10-K, read.

Costco runs a membership-warehouse model that produces recurring fee income and loyal repeat traffic: paid members rose to 84.1 million from 81.0 million, renewal rates were 92.3% in the U.S. and Canada, and Executive members (who drive most sales) reached 42.3 million. The business is still expanding, with 939 warehouses at year-end, but it depends heavily on U.S. and Canadian results, its valuation assumes continued strong execution, and it faces rising competition and leadership turnover.

• Heavy concentration in the U.S. and Canada, which generated 86% and 83% of net sales and operating income, and within the U.S. a dependence on California (26% of U.S. net sales).
• International operations, including Canada (27% of net sales but 35% of operating income), expose results to foreign-exchange swings, tariffs, and trade actions that can raise merchandise costs.
• Membership economics depend on renewal rates, which stood at 89.8% worldwide; any slippage in renewals or Executive upgrades would hit high-margin fee income.
• The filing says the stock price reflects high market expectations, so any shortfall in comparable sales, membership fees, margins, or openings could trigger a sharp share-price decline.
• Growing competition from Walmart, Sam's Club, BJ's, Amazon, and AI-driven shopping tools, which the company says may reduce loyalty or shift purchasing.

Not investment advice — general research, the same for every reader. You make your own calls.