Managing these risks requires greater care in selecting and training principals and other school leaders, and providing schools in unpopular locations with significantly more resources to remain attractive. When teacher allocation and promotion is governed by impersonal rules, those rules might result in suboptimal matches between teachers' talents and preferences on the one hand and the needs of schools and students on the other. Many systems combine multiple levels of governance precisely in order to avoid the dangers of both excessive fragmentation and centralisation. In most countries, schooling is principally a public-sector activity.