People are "awful at that" because when two people communicate, we're using a lot more than words. Each person participating in a conversation is doing a lot of active bridge-building. We're supplying and looking for extra nonverbal context; we're leaning on basic assumptions about the other speaker, their mood, their tone, their meanings; we're looking at not just syntax but the pragmatics of the convo (https://en.wikipedia.org/wiki/Pragmatics). The communication of meaning is a multi-dimensional thing that everyone in the conversation is continually contributing to and pushing on.

In a way, LLMs are heavily exploitative of human linguistic abilities and expectations. We're wired so hard to actively engage and seek meaning in conversational exchanges that we tend to "helpfully" supply that meaning even when it's absent. We are "vulnerable" to LLMs because they supply all the "I'm talking to a person" linguistic cues, but without any form of underlying mind.

Folks like your wife aren't necessarily "bad" at LLM prompting—they're simply responding to the signals they get. The LLM "seems smart." It seems like it "knows" things, so many folks engage with them naturally, as they would with another person, without painstakingly feeding in context and precisely defining all the edges. If anything, it speaks to just how good LLMs are at being LLMs.

Until we get LLMs with deterministic output for a given prompt, there's no guarantee that you and me typing the same prompt will yield a working solution of similar quality.

I agree that it helps to add context, but then again assuming people aren't already doing it doesn't help in any way. You can add all the context there is and still get a total smudge out of it. You can select regenerate a few times and it's no better. There's nothing indisputably proving which part of your prompt the LLM will fixate on more and which one it will silently forget (this one's even more apparent with longer prompts).