Exercise 1: The Backup Mistake Elena Almost Made — Possible Solution
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THE MISTAKE SHE ALMOST MADE
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Elena nearly skipped the option to encrypt her Time Machine backup disk, to save a step during setup, before remembering Chapter 9's own explicit warning: an unencrypted Time Machine backup would create a complete, unprotected copy of everything the FileVault encryption she'd just enabled in Step 6 was protecting on the original disk. If that unencrypted backup drive were later lost or stolen, it would expose all of that data just as fully as if FileVault had never been turned on at all.

WHICH EARLIER CHAPTER'S WARNING STOPPED HER
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Chapter 9's own warning about encrypting the Time Machine backup disk is what she recalled, directly connecting it back to the FileVault protection set up in Chapter 8/Step 6 of this capstone.

WHY THE CHAPTER FRAMES IT AS "THE MISTAKE SHE ALMOST MADE" RATHER THAN JUST DESCRIBING THE CORRECT STEPS
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Presenting it as a near-mistake, rather than simply stating "enable backup encryption," demonstrates that the earlier chapters' warnings are genuinely load-bearing in a real setup - not just facts to memorize, but the kind of thing a real person would actually be tempted to skip under real time pressure, and that recognizing the tempting shortcut and catching it is exactly the practical judgment the course was building toward, not just knowledge recall.

WHY THIS WORKS AS AN ANSWER
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It correctly identifies the near-mistake as skipping Time Machine backup-disk encryption, correctly ties it back to Chapter 9's warning connected to Chapter 8's FileVault setup, and explains why framing it as an almost-made mistake demonstrates practical judgment rather than just restating a fact.