Performance Management at work

Could you help me to think through how to apply The Model at a corporate job as a manager? Part of my job is to the assess and manage the performance of ten individuals. I have set performance expectations for my team, and there are certain members who are not meeting expectations. I prefer to be a non-judgemental leader, but I find myself feeling like I am “judging” when I am assessing. I feel guilty when I am providing constructive feedback or delivering a poor performance review because I am having a thought that I am being too hard on the employee or perhaps not knowing all of the facts and incorrectly assessing them. The employee tends to disagree with the feedback and provide a different perspective (which others tell me is an excuse). Could you help me to reframe my thoughts and/or help me think if judgement is different than assessment? Thank you!