They are named like this because you can use it for more than just errors, it just so happens that it's a good fit for errors. In fact, I wish Rust had named it Either, instead it's called Result (with Ok/Err variants). This is great for errors, but it leads to the creation of (https://crates.io/crates/either) because there are scenarios where you want Either and the Err/Ok name is too presumptuous.

A good way to remember which variant represents success in the case you're talking about an error is that Right is the "right" variant, Left is the "wrong" one.