Grasping the nettle
A former head often tells me, with a frequency that reveals how he dwells on the memory, that he allowed a caretaker to continue for years despite the fact that the employee was lazy and incompetent. He was, he admits, shying away from provoking a long-drawn-out grievance procedure.
I understand that, because I've never liked confrontation either. Teachers, by nature, are often fair-minded to a fault, and also assume that all colleagues are doing their best. Add the fact that schools tend to be collegiate rather than hierarchical and you end up with stories of staff emerging from disciplinary interviews unsure of whether they have been disciplined or not, so vague and conciliatory was the encounter.
What's the right thing to do
You are not in leadership to be popular. I can recall many times when, as a middle or senior leader, I should have made unwavering eye contact with someone and said unambiguously: "This is not a discussion. You must do this."