# Chapter 9 — Practice-on-your-own hints — Companion > Diagnostic hints for the Practice-on-your-own problems from Chapter 9 of The Defensible Decision. Canonical URL: https://www.thedefensibledecision.com/ch/09/practice/ [← Chapter 9 companion](/ch/09/) · [All chapter resources](/ch/) Short diagnostic hints for the two Practice on your own problems in this chapter. Attempt each problem before opening the hint. Complete answers appear in Appendix G of The Defensible Decision: Practice Workbook. ### Problem 1 — the reconciliation gap Restated: A Copilot-generated report cites a Q3 revenue number ($42.7M) that is close to but not exactly the number your finance partner uses ($42.9M). Which of the three failure modes is most likely firing? Name the sequence of checks you would run to isolate it, and the specific Add-to-page field-set inspection that would confirm. Show a diagnostic hint Diagnostic cue. Reconcile every headline measure to the BRD and source-of-truth query before trusting a polished report. Complete answers appear in Appendix G of The Defensible Decision: Practice Workbook. ### Problem 2 — the BRD-in-disguise Crystallize failure Restated: A colleague reports that they have run three Refine cycles on a Copilot report and the executive still says «this is not what I wanted.» Name why this is a Crystallize failure disguised as a Refine failure, and the specific reset move. Show a diagnostic hint Diagnostic cue. If the prompt leaves a BRD field implicit, make it explicit in Crystallize before Copilot builds. Complete answers appear in Appendix G of The Defensible Decision: Practice Workbook. ### Related on this site - [Chapter 9 companion page](/ch/09/) — further reading, self-check quiz, and the reconciliation activity. - [Prompt library](/prompts/) — the Crystallize prompt templates that make the reset move easier. - [All chapter companion pages](/ch/). - [Feedback](/errata/) — share corrections and improvement opportunities across all chapters. ### About the three-tier Practice format Each chapter of the book closes with a three-tier Practice block adapted from Cole Nussbaumer Knaflic's course-adoption pattern in Storytelling with Data: Let's Practice!: Practice with us (one worked problem with full solution in the book), Practice on your own (open problems with complete answers in Appendix G of the Practice Workbook; this page offers short diagnostic hints), and Practice at work (an open-ended prompt to apply the chapter's move to a live artifact). This page hosts the middle tier.