Fergius-Engineering The rule
Anything you depend on that a user can touch will get renamed, moved, deleted, and duplicated. If your code assumes a fixed path or a single copy, it breaks the first time the user does something ordinary. Before you finish, run those four actions through your head.
Fires when
Your code reads, writes, or depends on a file, a record, a document, or any state the user can edit outside your code.
How to apply
For each thing you depend on, ask the four questions: renamed? moved? deleted? duplicated?
Prefer finding things by type or id over a hardcoded path or name. Decide what happens in each case instead of assuming it won't happen.
Worked example
Your app stores its settings in a file at a hardcoded path. It works on your machine. Then a user renames the file, and the app silently writes a fresh one with defaults, losing their config. Or they copy the project folder, and now two copies fight over the same path. Looking the file up by a stable marker instead of a fixed name, and handling "not found" and "more than one" on purpose, turns four silent bugs into defined behavior.
Red flags
| Thought | Reality |
|---|---|
| "The file is always at this path" | Until the user moves it. |
| "There's only ever one" | Until they duplicate it. |
| "They won't rename it" | They will. |