People

A natural, inevitable disagreement arising when people's interests, ideas, or values differ; it is not inherently bad and can be managed constructively.

Constructive conflict surfaces ideas, improves decisions, and strengthens the team; destructive conflict damages relationships, morale, and progress.

Because openly addressed disagreement reveals better solutions and builds trust, whereas suppressing it lets problems fester.

Schedules, project priorities, resources, technical opinions, cost, personalities, and administrative procedures.

Personality conflicts, because they are interpersonal and not resolved by data or schedule changes.