Why not the "start of something bad"?

[Haihao from Japan]

English Idioms and Expressions, Advanced Level

ESL/EFL Test #15 "Teaching your Family to Drive", question 5

Although he only asked me to lend him EUR 5, I could see this was the thin end of the wedge.

(a) start of something financial
(b) start of something easy
(c) start of something worse
(d) start of something difficult

English Idioms and Expressions, Advanced Level

ESL/EFL Test #15 "Teaching your Family to Drive", answer 5

Although he only asked me to lend him EUR 5, I could see this was the start of something worse.

Correct answer: (c) start of something worse

Your answer was: incorrect
Although he only asked me to lend him EUR 5, I could see this was the start of something easy.
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Hi,

I could understand c) was the best for the context but my problems were:

1. Why not the start of something bad? If worse, what does it imply (than what)?
2. What is the original meaning of 'thin end of the wedge'? Could it suggest 'start from the small and go to the big'?

haihao

[Mister Micawber]

.
Lending 5 euros is bad; subsequently lending 50 euros is worse.

A wedge is a triangular steel or wooden tool which is driven into an aperture (for instance, a crack in a log) to widen the aperture or split the log. The narrow end is inserted first, and then blows of a mallet force thicker sections of the wedge into the gap. But A PICTURE IS WORTH 1000 WORDS.
.
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Native English teacher at Mister Micawber's

[Alan]

Hi,

The idea of 'worse' behind the expression is that things are going to become worse - the thin end in contrast to the fat end shows what is going to happen.

A
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English as a Second Language
You can read my ESL story Present Simple