Exercise 2: Why "Add the Missing Index" Is the Wrong Place to Stop — Possible Solution
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THE 5-WHYS CHAIN, PER THIS CHAPTER
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Why did checkout fail? A query ran forever. Why did it run forever? It
scanned the whole table. Why did it scan the whole table? No index
existed on the filtered column. Why wasn't there an index? "The
schema-review process for new queries doesn't currently check for
this."

WHY "ADD THE MISSING INDEX" ONLY ADDRESSES THE PROXIMATE TRIGGER
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Per this chapter, the proximate trigger is "the immediate, final
action that set the incident off" - in this case, the specific
unindexed query. Adding the index fixes that one specific query,
resolving today's specific incident, but it doesn't touch the process
that allowed an unindexed query to reach production in the first
place.

THE ACTUAL ROOT CAUSE
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Per this chapter, "that last answer - a missing schema-review check -
is the actual root cause worth fixing." The systemic gap is that
nothing in the current process checks new queries for missing indexes
before they ship - a condition that will produce the exact same class
of incident again with the next unreviewed query, regardless of
today's specific index being added.

WHY THE DISTINCTION MATTERS PRACTICALLY
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Per this chapter, "'add the missing index' fixes today's incident; it
does nothing for the next query that reaches production the exact same
way." Stopping at the proximate trigger produces a review that looks
complete but leaves the actual systemic vulnerability untouched -
exactly the failure mode a genuinely useful review is supposed to
avoid.

WHY THIS WORKS AS AN ANSWER
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It walks through the actual 5-whys chain from the chapter, correctly
distinguishes the proximate trigger from the root cause, and explains
specifically why stopping at the trigger leaves the recurring
vulnerability unaddressed.