Build spacing on a consistent scale

Why this rule exists

When the gaps in an interface are arbitrary, six here, eleven there, fourteen somewhere else, the eye cannot find a rhythm, and the design feels subtly off even to people who would never notice the numbers. A spacing scale is a small set of allowed values, usually multiples of one base unit, and every margin, padding, and gap in the product is drawn from it. This does for space what a type scale does for size: it replaces a thousand tiny judgments with a handful of consistent decisions, and consistency is what the eye reads as intentional. It also makes the work faster and more durable, because designers and engineers stop debating whether a gap should be thirteen or fifteen and simply reach for the next step. A system you can name is a system you can keep; a pile of magic numbers is one nobody can maintain.