Exercise 2: Why "Same Underlying System" Predicts What a Custom Post Type Is — Possible Solution
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WHAT THIS CHAPTER MEANS BY "THE SAME UNDERLYING SYSTEM"
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Per this chapter's own finding-box, "Posts and Pages aren't stored in
two separate systems - they live in the exact same underlying database
table, distinguished by a single column that records which 'post type'
each row is." In other words, the difference between a Post and a Page
isn't a difference in WHERE the data lives or HOW it's stored - it's
just a label (a value in one specific column) attached to an otherwise
identical row of data.

WHY THIS MATTERS FOR UNDERSTANDING CUSTOM POST TYPES
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If "Post" and "Page" are really just two different values that single
column can hold, then nothing about the system inherently limits it to
only those two values. Per this chapter, "WordPress Intermediate/
Advanced 4 shows that this same mechanism is exactly what lets a
developer define an entirely new, custom content category beyond just
these two." A custom post type, then, isn't some separate, exotic
feature bolted onto WordPress - it's the exact same shared table and
mechanism, just registered with a third (or fourth, or fifth) label
instead of only "post" and "page."

WHY THIS PREDICTION IS MEANINGFUL, NOT JUST A GUESS
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Knowing this in advance means a custom post type shouldn't be expected
to behave like some fundamentally different kind of content requiring
entirely new concepts to understand. It should be expected to behave
similarly to Posts and Pages already do - having a title, content,
possibly categories/tags, possibly hierarchy - because it's built from
the exact same underlying storage mechanism this chapter already
introduced, just given its own distinct label.

WHY THIS WORKS AS AN ANSWER
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It restates the chapter's own explanation of the shared table/column
mechanism precisely, explains the logical consequence (nothing limits
that column to only two values), and connects that consequence directly
to what should be expected from a custom post type before it's ever
formally introduced.