Static variables are available throughout the entire life of a program. They are allocated in a block of memory known at compile time. Due to that, they tend to represent global state that the program can access. It's getting especially tricky if one static variable depends on another. Some language communities even talk about static initialization order fiasco (looking at you, C++). Other, like C, allow static intialization only with constant literals/expressions. Rust belongs to this group as well. But there are alternatives...