"What might have appalled us when we'd started our trip just a few days ago no longer impressed us much"

I came across this sentence from a book about a journalist:

What might have appalled us when we'd started our trip just a few days ago no longer impressed us much.

It is confusing for two reasons. It isn't clear how the different clauses fit together. Secondly impressed seems like an odd word to use here. It doesn't seem to fit according to the definitions from Google:

1. make (someone) feel admiration and respect.

Their performance impressed the judges

2. make a mark or design on (an object) using a stamp or seal.

The company should impress the cards with a stamp

... or the definition from Cambridge Dictionaries Online:

to ​cause someone to ​admire or ​respect you:

Maybe it does fit, but it is not clear how.

Can you explain this sentence?

Solution 1:

The sentence is from A Passage To Africa by George Alagiah (2008)

What might have appalled us when we'd started our trip just a few days ago no longer impressed us much.

The sentence has a fused relative construction as a Subject. The structure of the sentence is:

• [X] no longer impressed us much.

The phrase beginning with what in the fused relative construction is basically a special kind of relative clause. It does not have an antecedent noun to tell us what the clause is modifying. We can understand the word what as meaning the thing which or the things which. We understand the fused relative to mean:

• The things which might have appalled us ....

This means we understand the sentence like this:

• The things [ which might have appalled us when we'd started our trip just a few days ago ] no longer impressed us much.

The author was a journalist in Somalia during the Somali civil war. As a journalist, Alagiah was seeking out the most shocking images he and his cameraman could find. The war in Somalia provided many, many shocking stories and images. Alagiah is giving us an insight into the uncomfortable reality of the psyche of a war journalist. As he got used to seeing more horrific things, they were no longer shocking enough. The new story or the new picture had to be more shocking than the last one. So things that shocked him when he started his trip didn't shock him or make an impression on him any more. Here the use of the word impressed means to have a forceful effect on someone's mental state. It does not mean "to create a good impression".