The 'S' in SOLID. A unit of software should be interested in doing one thing, so it only has to change in rare circumstances. Bellware frames all design principles — SOLID, DRY, Liskov substitution, tell-don't-ask — as really being about managing change: putting things that change in places that change, and keeping things that shouldn't change in places that aren't expected to change, to limit the blast radius of modifications.