An organisation runs discovery by having a researcher interview customers alone and circulate a written summary to the product manager, the designer and the engineer. On Torres's account of the trio, what is missing?

The principle — the trio's product is a shared understanding, and a shared understanding is not a document.

Why the key is correct — Torres's claim is that When a product trio works together to develop a shared understanding of their customer, they are in a much better position to create products that customers love. Working together is the mechanism. Three people who sat through the same interviews disagree about different things afterwards than three people who read the same summary, because each of them noticed what their own discipline made visible.

Why the others are wrong — a circulated summary moves conclusions and leaves the evidence behind, so the engineer never hears the sentence that would have changed the design. A formal sign-off adds governance to conclusions nobody in the room witnessed. And the presence or absence of a designer is beside the point when none of the three was in the research.

Remember this — the trio is defined by doing the work together, not by receiving the same report.

Sources — Teresa Torres on the product trio, Product Talk.