Ownership, borrowing, and lifetimes is a huge topic. There's way too much in this "intro" guide alone for you to absorb everything in it at once. So occasionally circle back and revisit the common misconceptions, or the documentation on variance, or take another crack at some complicated problem you saw. Your mental model will expand over time; it's enough in the beginning to know some things exist and revisit them when you run into a wall.
Moreover, Rust is practicality oriented, and the abilities of the compiler have developed organically to allow common patterns soundly and ergonomically. Which is to say that the borrow checker has a fractal surface; there's an exception to any mental model of the borrow checker. So there's always something new to learn, forget, and relearn, if you're into that.