Fairness should not depend on how much you like the person involved.

Fondness is a powerful and invisible thumb on the scale. The same behaviour reads as a lapse in someone you like and a pattern in someone you do not, and the reasoning arrives so smoothly that it never feels like bias. That is the whole difficulty; partiality does not present itself as partiality.

A useful test is to swap the name. Imagine the same act done by the person you least want to defend, and by the person you most do. If your conclusion changes, the conclusion was about them.