When a people problem is a structure problem
Repeated conflict between capable people usually points at unclear authority, not character.
When two competent people keep colliding, the instinct is to treat it as a personality conflict. More often the organization has never decided who owns the call they are both trying to make.
People fight over decisions no one has been given the authority to make.
What to look at first
Before addressing the relationship, look at decision rights, role boundaries, and how work moves between the two functions. Clarify those, and a surprising share of the friction disappears without a difficult conversation.
If the friction remains after the structure is clear, then it is genuinely a leadership or behavior issue, and it can be addressed directly without ambiguity about who was right.
