We are (mostly) not writing for stupid people, at least in my field. We might be writing for ignorant people, busy people, hurried people-but not stupid people.
Don't write down.
Pictograms from IKEA are not meant to indicate you are stupid; they are meant to cover the fact that you might not know how to put that piece of furniture together (and that you don't speak the same language as the designer). But they don't write down.
Unless it's a field where this document is life or death, leave out what you can.
But don't write down.
You gain nothing by assuming the reader is stupid. They might be ignorant or forgetful, but (with rare exceptions) you don't gain anything by treating them like they're stupid.
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