Jon Aizlewood on the process of creating a design system:
Good design systems start with a vision. A creative direction before they become a thing. They need to have the relationships between elements worked out. The hierarchies, grids and layouts need to flex and scale. Proximities, similarities and placement need examining. Gestalt theory has to get applied. None of these things are possible if you start with a loose collection of bits.
This is what differentiates a style guide from a design system — or as it's positioned in the article, are you designing components or are you designing a system?