El que no sabe es como el que no ve

10:29 Mar 16, 2015 

Hear, hear!

10:22 Mar 16, 2015 

this could be an ironic take on "What the eye doesn't see, the heart doesn't grieve over" (ha ha!).

But seriously, this context SHOULD have been posted right from the start, as most if not all of our suggestions are now way off the mark - i.e., they might work somewhere else but are inappropriate for this context. I know I bang on about questions without context, but this is a classic example of how important it is: we've all been groping in the dark with this one...

As for the maid, I think she's just as likely to reply with something along the lines of "Well, that just goes to show how little/much I know about fashion these days!" or "Now I'm showing my ignorance!" as she is to come out with some really pithy idiom. OK, I guess you're looking for a snappy riposte, but there was no hint of this in the question posted.

07:19 Mar 16, 2015 

In that situation, she might simply say "Oh, my mistake" (or "my bad"). Or possibly "It's all Greek to me" (meaning I just don't understand that world).

I think Carol's "There are none so blind", or indeed my own "Ignorance is bliss", would sound idiomatic, but the maid would be making a different point.

03:01 Mar 16, 2015 

A designer (a man) is talking with a maid. The designer shows her a fancy dress and she says, "the dress is beautiful but, there is a sleeve missing". The designer tells her that his intention was to create a the dress with one sleeve only. So she says "El que no sabe es como el que no ve". I guess she admits her ignorance about the trends of the fashion world.

22:23 Mar 15, 2015 

...who is saying it and in what circumstances
Perhaps you could tell us asker?

21:45 Mar 15, 2015 

Do you think he could just say, "blind ignorance"

19:37 Mar 15, 2015 

to the extent that there is a trade-off here. I don't think there is an idiom with this meaning. So you can either have an idiom with a different meaning, such as "There are none so blind as those who will not see" or "Out of sight, out of mind", or (one that nobody has suggested) "Ignorance is bliss", or you can have a non-idiom with the same meaning. It depends, as Carol says, on whether the priority is to be accurate or to be idiomatic. But none of the three idioms mentioned above is even approximately accurate as a translation of this Spanish phrase and in most contexts I don't think they'd be viable translations.

17:45 Mar 15, 2015 

on how the phrase is being used