The meaning of "They know who they are"

Question

I'm reading a programming book and in it it is said, of a subset of engineers,

"Electrical engineers and systems designers who create computer motherboards and other hardware systems incorporating Intel processors need to know some of the rest, but they are a small and hardy crew, and they know who they are."

I unsuccessfully tried to find the meaning of that last bit on its own online. It seems to be an idiom. I would guess that it means that due to the small size of the group, the prominent people in it are known to one another and comprise a sort of community. Perhaps someone knows/has encountered the segment in question?

Juhasz · Accepted Answer

The phrase "they/you know who they/you are" is typically used to address members of a subset of your audience without specifying their names.
We often use this phrase in an acknowledgement, or dedication, like you might find at the beginning or end of a book.  An example would be:

This book is dedicated to all the people who supported me as I was writing it.  They know who they are.

In other words, those people who supported me know that they are included in the group "all the people who supported me", so I'm not going to list each of their names.
Another common use - and one that perhaps makes more sense - is when you're admonishing a group of people in public, but want to spare them the embarrassment of being singled out.  For example:

Some people have not yet completed the required training - they know who they are (because we sent them a reminder email) - and we're working with them to get the training finished as soon as possible.

Similarly, you might use this phrase when giving a public address because you want the general audience not to worry that you might be talking about them:

For those of you who forgot to sign up for a shift - and you know who you are - please email Alice by the end of the day.

In the quoted example, the author intends to say something like this:
The next section is not for everyone.  It's only for people who need to know extra information about [whatever the next section is about]. The people who need to know this information are electrical engineers and systems designers who create computer motherboards and if you were a member of this group, you would know you were a member.  So if you're not sure if this next section is for you, it's not.

user416741 · Answer

It is an idiom. It stands for “I am not mentioning their names [to avoid embarrassment, argument etc] but those people know I am talking about them”. It is often said in a lighthearted way.

jamesqf · Answer

It means that the people in the group know that they're in the group, not that they know each other, or that the speaker knows them. In the example, people doing that particular sort of hardware design know that they need to know the particular technical stuff the author's writing about, while other people really don't. But they generally aren't known to each other: if I design motherboards for a US-based company, I probably have no idea who my counterparts designing them for Chinese-based companies are.

Answered by jamesqf on July 20, 2021

The meaning of "They know who they are"

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