When is it appropriate to use `panic!` in Rust code compared to returning a `Result`?

Use `panic!` when facing a critical, unrecoverable error that signifies a bug in the program logic, such as an out-of-bounds array access (if not caught by other means), a failed `assert!` or `debug_assert!`, or an `unwrap()` or `expect()` call on a `None` or `Err` value that you confidently believe should never occur. `Result` should be used for anticipated failures that the caller is expected to handle, like file not found, network connection issues, or invalid user input. `Result` promotes robust, fault-tolerant applications.