But the Queen is smarter.
Communication of good structured content between willing parties is key to a successful kingdom.
Sometimes that content is ahead of the rules that the King has proclaimed.
The Queen, with her ability to persuade the King, changes the rules of the schema to conform to the instance that the people want to use.
The Lesson:
The instance is far more common, directly useable, and malable to new requirements. People will change content, adding in their own structures, without knowing or caring that the schema does not reflect these new requirements. Taking this into account, schemas should be instructed by the content people want to encode rather than restrict what they can encode.
In summary, start with the document you want to model and not with the schema. The schema is an artifact of constructing those instances and describes a class of instances similar to your content.