I stopped guessing about CSV files from five vendors

Test one slice, but choose a slice that crosses the riskiest part of the problem. A tiny easy demo will only prove the easy part.

Use this decision rule:

• If reversing the choice is cheap, try it.
• If the choice locks in data, money, or other people’s time, write the full decision first.
• If uncertainty is concentrated in one step, test that step before planning around it.

For CSV files from five vendors, make the first test produce evidence you can compare, not just something that looks complete.