Sohan's grandfather grows wheat, then gets it ground into flour and sells it at the market

Why

Sohan is right that it all starts in the primary sector — growing wheat directly from land is exactly what that sector means. Where his rule breaks is treating the whole chain as one activity just because it began there. Each STEP in the chain is its own kind of work, sorted by what actually happens in it, not by where the raw material first came from. Growing the wheat is primary (using nature directly). Grinding it into flour at the mill is secondary (transforming a raw material into a new product). Selling that flour in the market is tertiary (a service — getting the product to a buyer). The same wheat passes through all three sectors on its journey from field to your kitchen. Test: trace a glass of milk the same way — a cow (primary), a dairy turning it into paneer or powder (secondary), and a shop selling it (tertiary), the AMUL model exactly. No, different parts are different sectors: one product can pass through primary, secondary and tertiary work on its way to you, and each step is classified by its own job, not by how the chain began.