When I went to uni, we had tutorials several times a week. Two students, one professor, going over whatever was being studied that week. The professor would ask insightful questions, and the students would try to answer.
Sometimes, I would answer a question correctly without actually understanding what I was saying. I would be spewing out something that I had read somewhere in the huge pile of books, and it would be a sentence, with certain special words in it, that the professor would accept as an answer.
But I would sometimes have this weird feeling of "hmm I actually don't get it" regardless. This is kinda what the tutorial is for, though. With a bit more prodding, the prof will ask something that you genuinely cannot produce a suitable word salad for, and you would be found out.
In math-type tutorials it would be things like realizing some equation was useful for finding an answer without having a clue about what the equation actually represented.
In economics tutorials it would be spewing out words about inflation or growth or some particular author but then having nothing to back up the intuition.
This is what I suspect LLMs do. They can often be very useful to someone who actually has the models in their minds, but not the data to hand. You may have forgotten the supporting evidence for some position, or you might have missed some piece of the argument due to imperfect memory. In these cases, LLM is fantastic as it just glues together plausible related words for you to examine.
The wheels come off when you're not an expert. Everything it says will sound plausible. When you challenge it, it just apologizes and pretends to correct itself.