Staying objective and away from any kind of biases may require sometime. It improves with practice. One need to know about his/her short comings, one's own traumatic experiences, unconscious thoughts. The more person is aware and knows hoe to keep professional self different from personal self, the more person moves towards objectivity.
Every human being can get triggered sometimes by a certain situation.
Self-awareness is key. When a person knows himself well enough, his strengths and weaknesses, his triggers and traumas and has worked on them, the easier it will be to recognize when one of them occurs.
I think being objective can be hard and is a skill in itself- one that people in this field need to hone. I think a lot it is about recognizing unconscious biases in yourself and working against them, keeping an open mind