Let's see if I can summarize the question correctly. I'm guessing that the question relates to a purportedly non-obvious combination of known things, X and Y.
In the background section, it seems some are inclined to describe both X and Y as known things. I don't do that. I try to determine which is dominant. For example, is it Y that improves X or X that improves Y. If it's a toss up, I just pick one (can't go wrong).
So, my background section describes only one, e.g., X. If you describe both, you're walking the reader (and the examiner) right up to your solution. You don't want the reader to be able to guess your invention after reading just the background section. That hints at obviousness.
Consider this example. USB drives are known. Bottle openers are known. People carry a lot of stuff in their pockets, including USB drives and bottle openers. What is needed is a way to allow people to carry both a USB drive and a bottle opener without consuming excess space in the people's pockets.
What's my invention? If you can guess, I've just laid the foundation for an obvious rejection -- all admitted prior art, including the motivation to combine.
On the other hand, if I just describe that bottle openers tend to be heavy and bulky and aren't convenient to carry in one's pocket because pockets tend to be fully of other stuff, the reader is left with much less of a hint at my solution. To the extent I feel the need to "introduce" the non-analogous, yet known, technology that provides the solution, I do so in the detailed description -- being careful to preserve the characterization of the other technology as "non-analogous" and to highlight the non-obvious recognition that the solution taken from the non-analogous art works in this different context.
Of course, many examiners don't actually read the applications they examine, so it's hard to say how much that helps in the PTO. However, attention to detail like that pleases clients and impresses litigators.