Fixation is an attention failure where the pilot locks onto one thing — the perfect shot, the battery figure, a single warning — and stops scanning everything else. The treacherous part is that fixation subjectively feels like concentration: you seem to be working with special care.
That is exactly what makes it dangerous: while you stare at the gimbal feed, you miss the approaching helicopter. The countermeasure is a deliberate scan cycle — drone, sky, screen, surroundings — and around again, for the whole flight.