Receiving a pull request from an outside contributor on GitHub is a significant milestone, but managing them can become challenging as a project gains prominence. The post by Mike McQuaid discusses various scenarios where it might be necessary to close pull requests, such as when a submission is out of scope, breaks integration tests, or is submitted to an unmaintained project. It emphasizes the importance of clear communication and documentation, such as a CONTRIBUTING.md file, to guide contributors on acceptable changes. Additionally, it advises on handling situations where discussions deviate from their original intent or become unpleasant, recommending closure to maintain project health. The post encourages project maintainers to thoughtfully consider each pull request's impact and not merge them out of obligation, highlighting that a project's responsiveness to contributions is a marker of its vitality.