Rust has a steep learning curve.
Once you're fully immersed in it, as with any skill, it becomes very difficult to properly remember what exactly made Rust difficult to learn. In a general sense, it could be the fact that it exposes the average programmer to some new features, most of them not present or only just beginning to show up in mainstream languages, and some that are close to unique.
You could also argue that Rust puts a lot of complexity in the writing process that tends to otherwise be left to later, which is a bit of a pretentious way to put it but is roughly true.
Learning Rust also involves a difficult-to-bridge gulf between intermediate and advanced simply due to a lack of resources. A lot of this can only ultimately be rectified by simply writing a lot of Rust, but since Rust somewhat lacks a well-known "go-to" usecase, learners are often approaching Rust with little to no obvious context in which to practice. There are options like the Advent of Code and Protohackers, which are excellent, but they can't be solutions for everybody.
I think we as a community need to seriously examine and agree on the underlying reasons for the bumps in Rust's learning paths, and work on fixing them. There are many excellent resources out there already, but there need to be many times more, especially in a wider variety of languages, and targeting a wide variety of learning styles and motivations.
Out of personal curiosity, I wanted to collect some data about people's experiences with learning and teaching Rust, because my perspective on what makes it challenging is inherently very limited. If you'd like to help, please leave your thoughts about your process in the comments, or link whatever you think might help. I'd greatly appreciate it.