where did the knife come from
A third-grade peanut butter sandwich assignment, and why it explains what people get wrong about prompt engineering.
In third grade I had to write a how-to for making a peanut butter and jelly sandwich. I thought I’d nailed it. Four steps:
- Get the bread.
- Get the peanut butter and the jelly.
- Spread the peanut butter on one slice, the jelly on the other.
- Put them together.
My teacher read it, looked up, and asked one question:
Where did the knife come from?
I had the vision. I’d skipped the environment. The knife was real in my head — I’d seen it in the drawer that morning — so I assumed it was real on the page. It wasn’t.
three phases of getting this wrong with LLMs
When I started taking prompt engineering seriously last year, I realized I was repeating the third-grade mistake. The arc was familiar enough that I think most people walk it.
Phase one: the one-liner. Single sentence. Expect the model to read your mind. When it fails, fight with it in the next turn instead of fixing the prompt.
Phase two: the notebook. Start saving prompts that worked. Notice that consistency matters. Notice that some prompts are doing work the model can’t actually do without more setup around it.
Phase three: the environment. Realize the prompt isn’t an instruction. It’s a room. The model can only use what’s in the room. If the knife isn’t in the room, the sandwich doesn’t get made — no matter how clearly you described the spreading motion.
what I write now
Three things stacked on top of each other:
- Context — where the ingredients live. What the model has access to.
- Constraints — how to use the tools, and how not to.
- Acceptance criteria — what “finished sandwich” actually looks like, in enough detail that the model can self-check.
There’s no magic word. There’s no clever phrasing trick. Prompt engineering is the same skill as writing a good bug report or a clear design doc: assume the reader doesn’t have your context, then put the context in the document.