59959
I was trying to tell a language-exchange friend that I didn't know something
with the somewhat express connotation that I should have (known).

The first thing that came to mind was しまう, which usually expresses unintended
action that is done. However, this immediately became a problem, as I did not
know how to use しまう with the negative て form. According to [this
topic](https://japanese.stackexchange.com/questions/22881/can-we-use-negative-
form-
before-%EF%BD%9E%E3%81%A6%E3%81%97%E3%81%BE%E3%81%86-f-ex-%E3%81%AA%E3%81%8F%EF%BD%9E%E3%81%A6%E3%81%97%E3%81%BE%E3%81%86
"Can we use negative form before ～てしまう : f.ex. なく+～てしまう？"), ないでしまう is
acceptable.

> **知らないでしまう**

Yet, this usage seems to be rather rare.

In short, if I were to say, "Oh, shoot, I didn't know that," what is the most
natural and/or common way to express this? Is 知らなかった alone enough?

よろしくお願いします。
CC BY-SA 4.0
2018-07-08T15:57:59.943
59958
2018-07-08T16:24:51.863
27674
question
grammar
Is 知らないでしまった a thing?
As you guessed at the end of your question, 知らなかった is actually enough to say,
in order to tell the person you're speaking to "I didn't know that."

知らないでしまう sounds very ungrammatical to me, and 知らなくてしまった doesn't sound much
better. The first sounds like you are asking the other person not to know
something, almost. The second sounds like you accidentally succeeded in not
knowing something.

to express "self reproach" or in other words, the "shoot" feeling, you don't
have to change the word 知らなかった, just intone it with emphasis. If you want to
truly emphasize that you feel chagrined, you could try elongating the last
syllable, but if you've never heard the way that sounds, you might end up
sounding very odd.

I might try to express this feeling with something like:

あ、そうか、そうか、知らなかった！

if you really want to say to the person that you "should have known that" you
can actually say so with:

知らなかった！知るべきだった(のにね)。

or

知らなかった！知ってたはず(なのに)。
CC BY-SA 4.0
2018-07-08T16:24:51.863
59959
2018-07-08T16:24:51.863
29347
59958
answer