A product manager must determine the optimal scope of their product by identifying the most valuable and concise subset of a user's workflow. This involves understanding the entire workflow, starting at the point where the product can add value, and stopping when the next step has well-defined market leaders or is done in multiple ways by different types of users. The product should focus on solving specific problems rather than trying to tackle an entire workflow from start to finish. Additionally, identifying and eliminating meaningless steps that don't add insight or decision-making opportunities for the user can help improve the product's overall value proposition.