Exercise 3: Why an Affiliate Product's "Stock" Isn't Real Stock — Possible Solution
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WHAT MAKES A SIMPLE PRODUCT'S STOCK QUANTITY "REAL"
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Per this chapter, a Simple product's stock quantity is automatically
decremented by WooCommerce itself as orders are placed through its
own checkout, and it can actively block or allow further purchases
(via stock status and backorder settings) once it reaches zero. It's
load-bearing: WooCommerce's own checkout logic reads and acts on it.

WHY AN EXTERNAL/AFFILIATE PRODUCT'S "STOCK" ISN'T
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Per this chapter, an External/Affiliate product routes the customer
straight to another site via a "Buy product" button, and never
touches WooCommerce's own cart or checkout at all. Since no order is
ever actually placed through WooCommerce for that product, there is
no checkout event to decrement a stock count against - any stock
quantity entered for it is purely informational for the store owner,
not a number WooCommerce's own purchase flow reads, enforces, or
updates automatically.

WHY THIS WORKS AS AN ANSWER
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It correctly identifies the mechanism that makes Simple-product stock
functional (automatic decrement and enforcement tied to WooCommerce's
own checkout), and correctly explains that this mechanism has nothing
to act against for a product type whose actual purchase never goes
through that checkout in the first place.