The usual explanation is a clock diagram. Here's a better one.
Sector rotation is normally taught as a cycle. Money moves from defensives to cyclicals to technology and back again, tracking where the economy sits. That is true enough at index level and close to unusable when you are looking at a single position.
Read through a supply chain it becomes concrete. Demand for AI applications shows up as cloud spend. Cloud spend becomes data centre capex. Capex becomes semiconductor orders. Orders become power contracts and grid connections. The signal travels down the stack, and it travels with a lag.
When the layer beneath yours is accelerating and yours is flat, something is being built that hasn't reached you yet. When your layer is running and the one beneath it has stalled, you may be looking at the end of a cycle rather than the middle of one.
Neither observation is a trade on its own. But they are questions worth asking, and sector membership never poses them — two companies in the same GICS sector can sit four layers apart.
The relationships are known. What's usually missing is a view that puts the layers side by side over the same window, so the sequencing is visible rather than inferred from memory. That is most of what this site does.