In our training classes, we emphasize the importance of solving market problems. Describing problems encountered by our target personas. It's the problem that drives product requirements. Yet we've become an industry of feature-speakers. "I want this and this and this and this!" Wait! What is the problem??
My friend Luke Hohmann wrote about this in his post "Market problems are still THE problem — even when you’re Agile!"
As teams embrace agile methods, some seem to have jumped backwards a decade, getting back to the thinking that opinions drive feature decisions; this is just wrong. Use market facts to uncover problems that customers are willing to pay to solve. Perhaps it's the pace of agile development, needing new items for the backlog every other week. Or perhaps it's a shift in the power of the "team" over the power of market facts.
If you're a product manager, you need to be delivering quantified market data to your product team; if you're a developer, you should demand it. Otherwise, the team will use their opinions of what they think people want. After all, in the absence of market facts, he who owns the compiler wins.