The naming, afaik, comes from the correspondence to the logical disjunction operator and so the constructors name the Left side of the disjunction and the Right side of the disjunction. Seems rather sensible to me.
That being said, I don't think it takes that much energy to remember that the right is the good value. If you are comfortable with monads, just remember that monads must be parameterized over a single type, and for Either that will be the right type (because we must partially apply the type constructor with the left type to get it down to the correct form).
And then clever guys come and use left as the good value, because then want to retry on error (as you can see in this thread). Plus it takes quite some energy to discuss the, well, unfortunate naming.
edit: I should specify that I mean when Either is used as a 'Result' type. There are plenty of other use cases you can use Either outside of Ok/Err values.