The most common issues are with ownership, lifetimes, and the borrow checker. If the person is an experienced C or C++ programmer they'll probably have an easi

The most common issues are with ownership, lifetimes, and the borrow checker. If the person is an experienced C or C++ programmer they'll probably have an easier time as you need some understanding of ownership and lifetimes to correctly use pointer-likes in those languages. The most likely issue here is that their mental model of ownership and lifetimes does not exactly match the borrow checker's. If they're coming from a language such as C# or Python, where you don't need to deal with these to anywhere near the same extent, suddenly being forced to reason about it just to pass the compiler can be bit of a hurdle.