Challenge 1: Why Whole-Object Keyframing Can't Bend Just an Arm — Solution Walkthrough

The answer:

Per this chapter's own material, Blender Fundamentals' own Chapter 8
keyframed an object's own whole-object transform — position, rotation,
scale — applied to the entire object as a single unit. A character's
arm bending at the elbow while the rest of the body stays still
requires posing just one part of a single mesh independently, which a
whole-object transform has no way to describe at all.

Why this genuinely needs a different tool:

Rotating the whole character object would rotate the entire body
together, not isolate the forearm's own movement around the elbow
joint specifically. There's no way to keyframe "just this part of the
mesh" using only the whole-object Location/Rotation/Scale properties
Chapter 8 covered.

Why rigging specifically solves this:

Per this chapter's own material, rigging adds an internal control
structure (the Armature and its own bones) specifically built for
posing individual parts of a mesh independently — exactly the
capability whole-object keyframing lacks, and exactly what this
chapter introduces to fill that gap.

WHY THIS WORKS AS AN ANSWER
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This exercise checks that the limitation of whole-object keyframing is
correctly understood, and that rigging is recognized as the tool built
specifically to solve independent, part-of-a-mesh posing.