Rust effectively forces you to code like you're writing a multi-threaded app even when you aren't. There's a reason why people suck at writing multi-threaded apps: because it's hard. This is what people are fighting when they fight the borrow checker. And this is why so many people find it frustrating. There's all sorts of designs that flat out don't work or are way more effort than they're worth.
It just turns out that mathematically proving GC-free code to be free of use-after-free and double-free errors is really difficult unless you disallow a lot of things.
https://doc.rust-lang.org/book/ch04-02-references-and-borrow...
> At any given time, you can have either one mutable reference or any number of immutable references.
In practice, this is unworkable enough that it would basically forces you to reference count the Foo, so you could preserve pointers across calls by incrementing the reference count.
On the other hand, Rust's approach is suboptimal in cases where you're using reference counting anyway, or are willing to pay the cost of reference counting.