Because the order follows cause backwards from what is visible. The line is the result: a tailing loop, an open loop, a fly that lands short. The rod movement is what shaped the line. The body movement is what moved the rod. Start with the symptom on the line, work back to the rod, and finish at the student’s body — the only place where a change can begin.

The order also decides what the student hears. Telling someone to move the wrist differently before they understand what the wrist is for asks for a change with no reason attached. Work the chain aloud: name what the line did, then what the rod did, then what the body did to produce it. Now the correction has a reason, and the student can check the result for themselves.

That is why the corrective half runs in reverse. Change the body movement, explain the rod movement it produces, then show the improved line. Diagnosis runs line, rod, body; correction runs body, rod, line.

Source

From Bruce Richards’ six-step fault analysis and correction; the exam uses it in Task 19; terms follow the FFI Fly Casting Definitions.