Exercise 1: Why a Partway Failure Points at Destination Space — Possible Solution
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WHAT THIS CHAPTER SAYS
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Per this chapter, "a restore that fails the moment it begins usually
points at something fundamental ... a restore that starts working and
then stops partway through more often points at something about the
environment running out mid-process - disk space, network bandwidth,
or a permission check that only trips on a specific later file."

WHY AN IMMEDIATE FAILURE IMPLIES A DIFFERENT KIND OF PROBLEM
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If a restore can't even begin, the problem is present before any data
has been written - something about the source file itself (corruption,
an unreadable format, a missing decryption key) is blocking the
process from starting at all. These are properties of the backup or
the initial setup, not something that depends on how much progress has
already been made.

WHY A PARTWAY FAILURE IMPLIES SOMETHING THAT ACCUMULATES OVER TIME
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Destination space is consumed progressively as a restore writes more
and more data - the process can succeed for a while, writing file
after file successfully, right up until the destination genuinely
fills up. That specific pattern - clean progress, followed by a
failure only once a threshold is crossed - is exactly what running out
of a finite, consumable resource looks like, and it can't produce an
immediate failure, because there's nothing to run out of before the
process has actually started consuming space.

WHY THIS DISTINGUISHES SPACE PROBLEMS FROM THE OTHER FAILURE MODES IN
THIS CHAPTER'S OWN TABLE
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A corrupted file, a lost decryption key, or a format incompatibility
would each be equally true before a single byte was restored - none of
them depend on how much has already been written, so none of them
naturally produce a "worked fine, then suddenly failed" pattern the
way space exhaustion does.

WHY THIS WORKS AS AN ANSWER
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It quotes the chapter's own reasoning, explains why an immediate
failure implies a pre-existing problem rather than one caused by
progress, and explains specifically why destination space is the kind
of resource that's consumed gradually - producing exactly the "starts
fine, fails partway" signature this chapter associates with it.