The Data Flow

This is the key insight: data flows from left to right, top to bottom. Each module takes input, does something, and produces output. That output becomes input to the next module.

Weather API outputs → Formatter receives that → Email module receives the formatted text → Sent.

No step can skip backward and pull from a step that hasn't run yet. The flow is always forward. This simple rule prevents most beginner mistakes—once you internalize it, data mapping becomes intuitive.