The languages trade complexity in different areas. Rust tries to prevent a class of problems that appear in almost all languages (i.e two threads mutating the same piece of data at the same time) via a strict type system and borrow checker. Zig won't do any of that but will force you to think about the allocator that you're using, when you need to free memory, the exact composition of your data structures, etc. Depending on the kind of programmer you are you may find one of these more difficult to work with than the other.