Few-Shot Beats Instructions When The Format Is Fussy

I spent an hour describing the exact CSV shape I wanted. Column order, quoting rules, how to escape commas inside a field, what to do with nulls. The model got it right maybe seven times in ten.

Then I deleted the whole paragraph and pasted two example rows instead. Ten out of ten, and the prompt got shorter.

Why it works: a format description is something the model has to reconstruct. An example is something it can pattern-match. Reconstruction is where the errors come from.

When to still use instructions: when the rule is about something that does not appear in the example — "never include rows older than 90 days" is invisible in a sample row, so it has to be stated.

Practical rule: examples for shape, instructions for policy.