Everything's in the title, but in other words, the following scenario: ```mermaid sequenceDiagram Author->>MR: pushes version 1 Author->>MR: assigns Marge MR->>Marge: picks up MR, fetches & rebases it Author->>MR: pushes version 2 Marge->>MR: pushes version 1 rebased ``` causes the last push from the author to be lost. Marge needs to fail when it tries to push and the remote was updated under its feet.