Exercise 1: Why the First Four Postulates Went Unquestioned — Possible Solution
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The first four postulates share a real quality the fifth one lacks:
each is short, simple, and describes something that's immediately,
intuitively obvious the moment you picture it - you can draw a line
between two points, extend a line, draw a circle of any size, and
recognize that all right angles look the same. Nobody needed a further
justification to accept them; they read as genuinely basic, foundational
facts about space itself.

The fifth postulate is structurally different. It's much longer, it
requires imagining two lines extended indefinitely far to see whether
they eventually meet, and its truth isn't something you can simply
glance at and confirm the way you can with "you can draw a circle of
any radius." Something that complicated, mathematicians reasoned,
looks more like the KIND of claim that ought to be a derived
consequence of simpler starting assumptions - a theorem, not a basic
axiom - rather than something so self-evident it needs no
justification of its own.

That structural difference (simple and immediately obvious vs. long,
conditional, and requiring imagination of an infinite extension) is
exactly why the first four were accepted without a second thought while
the fifth attracted two thousand years of attempted proofs.

ANSWER: The first four postulates are short and immediately, intuitively
self-evident on inspection, while the fifth is long, conditional, and
requires imagining lines extended indefinitely to check - a structural
difference that made the fifth look like it ought to be provable from
simpler assumptions, rather than being a basic assumption in its own
right the way the first four clearly were.

WHY THIS WORKS AS AN ANSWER
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This identifies the real structural/complexity difference between the
postulates as the actual reason for the differing scrutiny, rather than
just restating that the fifth "seemed less obvious" without explaining
why.