>> The hardest single part of building software system is deciding precisely what to build. ... Therefore the most important function that software builders do

>> The hardest single part of building software system is deciding precisely what to build. ... Therefore the most important function that software builders do for their clients is the iterative extraction and refinements of the product requirements. For the truth is, the clients do not know what they want. What's the role of the product managers here. In common experience, how much of the above falls on the product managers vs. the software builders?