Rust’s ownership model is used to provide memory safety. Entities have only one owner so that the compiler can reason about when they go out of scope and can be safely dropped. If x didn’t get invalidated by the move then both x and y would own the entity. You could then do something like pass y into a function that would drop y at the end of the function scope, and then cause a use-after-free by using x. With the ownership model the compiler can guarantee that use-after-free is always a syntax error. The ownership model is a fair bit more complicated than this, but move semantics are at the core of it.