To build a single source of truth for ecommerce data, you need four things in sequence: a unified integration layer that pulls from every channel without manual work, a normalization layer that applies consistent metric definitions across all sources, a governance agreement on what each metric means and who owns it, and a reporting layer that every stakeholder uses instead of building their own. Most brands attempt this in the wrong order. They start with a dashboard and work backward, which is why they end up with a beautiful display of numbers that nobody agrees on. The sequence matters. Build the foundation before the interface, and the single source of truth becomes real rather than aspirational.