What's interior mutability and why do you think it's bad?

I might have another try at rust some time in the future. I think I tried it in a bad situation having to use it for a web microsevices project when I had limited knowledge of the language. If it had been another language I probably would have been able to pick it up in the time frame required. Using it did cost me in terms of grades, and it was a poor decision to use that language at that time.

The main things I struggled with were all the borrow checking and asynchronous stuff, as well as the lifetimes concept. I still don't understand how you are meant to specify object lifetimes. In C you assign and free things manually, in Java and Python it's done mostly automatically, in C++ you choose manual or automatic when it's assigned. In Rust it seems it's automatic until the compiler can't figure it out and then it becomes manual, which is frankly bizarre.