Big same. I remember being not being able to share a reference to something allocated on the stack at the start of main to a background thread. I was like "come on, of course its safe. That was allocated before the thread was spawned. It's main. When it returns the application exits"

But rustc's error messages helped it click that there might be a race condition on when the application returns from main and the background thread terminates. So it really needs to have the static life time to be safe. It's a small subtle thing but depending on the application it could lead to real bugs. I've definitely written variations of that bug in C before. A newer dev would have just accepted that flat out without arguing.

I've found Rust useful to study while I'm doing my primary job in C++.

A lot of the features Rust offers regarding traits and types can be emulated in C++ with templates, but the way C++ does it is far more obfuscated. Seeing the same thing implemented in Rust helped me wrap my head around what some complicated template nestings were doing ("Oh, this is implementing traits!") in our C++ code.