I have a similar experience. I initially naively thought that implementing data structures would be a good exercise in grasping syntax and ownership. It's usually one of the earlier exercises I do in learning a new language.

However data structures in Rust are not at all straightforward. Especially implementing traits, such as an Iterator for a Hashmap. And std implementations use loads of unsafe so beginner me became increasingly confused as to whether these things were not expressible in safe rust.