Vassal opinions are paramount to a stable realm. Low opinions can lead to factions forming against you, potentially resulting in civil wars. Use your Chancellor's 'Improve Diplomatic Relations' task, send gifts, grant honorary titles, and arrange advantageous marriages for your vassals. Avoid revoking titles or imprisoning vassals without a strong 'Reason' (hook or crime), as this generates tyranny and severely damages opinions across your realm. Keep powerful vassals happy.
