Impartiality and fairness is a standard and goal you strive for. Just because you can never attain that platonic ideal of it doesn't mean we should chuck it out the window and give into our biases. I hear people say something like this a lot to effectively say since it is impossible, there is no point in striving for it (not saying you are making this argument). But something I like to point out is impartiality is a skill. And while zero or few humans ever probably get 100% on that, it is easy to see in real life people who are more impartial and people who are less impartial. It is a skill you can cultivate and a skill you are always working on. I think in a game like D&D, when I started I was very much not an impartial GM. I wasn't mature enough. As I got older, as I got more experience, I did become much more impartial. I can see this in how I run games. I can also see the difference between GMs I encounter where there may be one who is quite good at being an impartial GM, but another who isn't. So all people really are saying when they talk about being an impartial ref is to strive to be the the former rather than the latter. I think the biggest danger here is to have too much faith in your own impartiality. You have to be open minded enough to review calls you made that might not have been free of bias or that weren't even-handed.