That is true of `&mut T`, but `&mut T` is not the only way to do mutation in Rust. The set of possible safe patterns gets much wider when you include `&Cell<T>`. For example see this language that uses its equivalent of `&Cell<T>` as the primary mutable reference type, and uses its equivalent of `&mut T` more sparingly: https://antelang.org/blog/safe_shared_mutability/