In teaching lower-division lit classes, when we're explicating a poem in class, I'm just about guaranteed to get this question at least once: "How do you know the poet meant to put all that symbolism in there? Maybe he was just trying to write a poem" or "Did he write the poem first and then put in the symbolism?"
My response is always "That's a good question," because it is. We talk about the poem, and about the revision process, and about what some poets have said about their writing processes. Sometimes those who write fiction or poetry will chime in.
In upper-division classes, though, students don't always ask that question. In those classes, I usually assign critical readings to accompany the primary texts, which can lead to a different set of responses about whether a particular essay helps to explain the text or seems just plain bonkers.
The problem is that, like the "did the poet really mean all this stuff?" question, talking about the critical approaches can derail discussion of the text. They're happy to talk on an abstract level about why a critical approach works well or works poorly, but then I say, "What about this passage on p. 59? Why does the text go in this direction?" or, more broadly, "What did you think about/make of this passage?" or "What is X that's mentioned here?"
Then . . . crickets. I'm comfortable with pauses and waiting while they look again at the passage, and sometimes, if they're struggling, I'll talk them through it.
It's a balancing act, trying to talk about both while not slighting either. That's what made me think of Frost's "Neither Out Far nor In Deep." The poem has a totally different meaning, of course, but on the days when the discussion doesn't work as well as it should, the phrase sticks in my head as exemplifying where it went awry. We didn't go "out far" (criticism) or "in deep" (text). On good days, we can do both.