Occasionally, these two readers turn out to be different people, when they should be the same. But, your words will reveal all ... if you're prepared to look at them objectively.
Let me give you an example. A student was targeting a weekly women's magazine. So, you'd be right in thinking that the core readership of this publication is female. But, the student wasn't thinking of a female readership as they wrote the following line:
It's at this point that your wife walks in.
Here, the words your wife suggests that whilst the writer was trying to write for a female readership, in their mind the reader they were trying to please was male. Generally speaking, only male readers will be able to identify with those moments when your wife walks in.
Of course, this situation is easily rectified, because you simply change the phrase to your husband or your partner.
Another example is this:
We all know what it's like taking our young children abroad on holiday.
That sentence suggests that the reader is talking to other parents with young children. And in a magazine read by parents with young children the reader will be able to identify with this - indeed, the reader will probably feel that this writer is 'one of them' and knows what she's talking about. However, the publication targeted was not one read predominantly by parents with young children, but older parents whose children have flown the nest.
The phrase, We all know clearly sets the writer as writing for people of her own age, when the readership of the target market was older than that.
That doesn't mean to say that this idea was inappropriate for this readership. It's quite possible that these readers may have young grandchildren now, and would be interested on some practical ideas about how to keep them entertained whilst on a two, or three, hour flight. Again, the solution is simple. A slight tweaking of the sentence will skew it in favour of the target readership.
We all know what it's like taking young grandchildren on holiday.
Now the reader will feel that the writer is talking to them.
In your first draft, points like this don't matter. It's important to get your piece written. But when it comes to editing, just remember who your target reader is, and ask yourself the question: Is it your target reader sitting in your head, or is it someone else? A few judicious tweaks of your text could make it much more appropriate for the readers of your target publication.