When talking with reasonable people, they will tell you if they don't understand what you're saying.
When talking with reasonable people, they will tell you if they don't know the answer or if they are unsure about their answer.
LLMs do none of that.
They will very happily, and very confidently, spout complete bullshit at you.
It is essentially a lotto draw as to whether the answer is hallucinated, completely wrong, subtly wrong, not ideal, sort of right or correct.
An LLM is a bit like those spin the wheel game shows on TV really.