used for saying that what happens next is disappointing or unpleasant。只不過卻 (表達出失望並且否定前句)
I tore open the box, only to discover that some of the parts were missing.
used to introduce a statement that indicates the only person or thing that is not included in or referred to by a previous statement。「除了某東西」的意思，後面的 for 可以省略，也可換成其他介詞（如 in, to, from）
He does nothing except (for) complain.
Employees were not allowed to leave except in an emergency.
She didn’t leave the house all weekend, except to go to church.
[=unless there was an emergency]
Take no orders except from me.
except (for/that) 特殊用法
used to give a reason why something is not possible or true。要不是/但是 （否定前句，然而相較於 only to，不一定是失望，有時也用於慶幸）
要不是: They would all have died except for [=but for] her and her quick thinking. (否定前句，指出「事實上」他們沒死，既然和事實相反，那就要用 would have 假設語氣)
但是: I want to go, except that I’m tired. (否定前句，指出他沒辦法去）
We would like go, except (that) it’s too far. (否定前句，指出我們沒辦法去）
only that = except that
只不過: He is correct, only that some details are omitted.
只可惜: This suit fits me well, except that the trousers are too long.
used to introduce a statement that adds something to a previous statement and usually contrasts with it in some way。然而（連接詞，不一定好或壞的對比用法）
She played well, yet she didn’t qualify for the finals. （轉壞）
He’s overweight and bald, (and) yet somehow, he’s attractive. （轉好，有時會加上 and 來中斷語氣）