6. Cavalier King Charles Spaniel
Unlike working breeds selected for field performance, humans bred the Cavalier King Charles Spaniel for centuries as lap warmth and royalty companion pets. These gentle spaniels lack working instincts that promote independent problem-solving in isolation. Instead, their genetic makeup urges them to seek continuous human contact. When left alone, Cavaliers frequently experience profound emotional distress, leading to persistent crying, house-soiling, and passive depression.