I'm not sure how you ended up on that page... my comment above links to https://simonwillison.net/2025/Jun/27/context-engineering/

The "Read large enough context to ensure you get what you need" quote is from a different post entirely, this one: https://simonwillison.net/2025/Jun/30/vscode-copilot-chat/

That's part of the system prompts used by the GitHub Copilot Chat extension for VS Code - from this line: https://github.com/microsoft/vscode-copilot-chat/blob/40d039...

The full line is:

  When using the {ToolName.ReadFile} tool, prefer reading a
  large section over calling the {ToolName.ReadFile} tool many
  times in sequence. You can also think of all the pieces you
  may be interested in and read them in parallel. Read large
  enough context to ensure you get what you need.

That's a hint to the tool-calling LLM that it should attempt to guess which area of the file is most likely to include the code that it needs to review.

It makes more sense if you look at the definition of the ReadFile tool:

https://github.com/microsoft/vscode-copilot-chat/blob/40d039...

  description: 'Read the contents of a file. Line numbers are
  1-indexed. This tool will truncate its output at 2000 lines
  and may be called repeatedly with offset and limit parameters
  to read larger files in chunks.'

The tool takes three arguments: filePath, offset and limit.