Exercise 3: Why the Black-Screen Problem Returns After a Reboot — Possible Solution
====================================================================

Explanation:

This is exactly the confusion the chapter's own warn-box describes
directly. Appending nomodeset via 'e' at the GRUB menu is a genuinely
real, live edit -- it did fix the boot for that one specific session,
and the user's confirmation that "it works" was entirely correct in
the moment. But per the chapter's own repeated point, an edit made
this way through 'e' is never written to disk anywhere -- it exists
only in memory, for that single boot, and is completely discarded the
instant the system is powered off or rebooted again.

When the user reboots later, GRUB reads grub.cfg fresh, exactly as it
always does, with no memory whatsoever of the nomodeset parameter that
was typed in during the previous session -- there was never anywhere
for that information to persist between boots. The system boots with
the exact same unmodified configuration that caused the original
black-screen problem, so the same underlying issue (the broken/
unsupported graphics driver) reappears, completely unchanged, because
nothing about the actual boot configuration was ever altered
permanently. The fix genuinely worked; it simply was never saved
anywhere for GRUB to reapply automatically on the next boot -- exactly
the "temporary but genuinely real" nature of a live 'e' edit the
chapter is explicit about.

WHY THIS WORKS AS AN ANSWER
------------------------------
This explains the mechanism precisely (a live edit exists only in
memory for one boot, never written to grub.cfg or any file), directly
tying the explanation back to the chapter's own warn-box rather than
just restating that live edits are temporary without explaining why
that specifically causes this exact symptom.