A schema learned by walking it: counts accumulate hop by hop from whichever object you start at, and each of the five relationship shapes every CRM is built from can be studied alone.
Seven objects, five relationship shapes — and what one record reaches.
The Account is the hub: almost everything hangs off it. The two shapes people miss are N:M, which needs a junction object of its own, and poly, where one field points at several object types.