This we learn from a recent posting at herdingcats:
"We must be crystal clear here. Requirements may emerge, but the needed capabilities at the needed time are a critical success factor for any project, no matter the domain. As Yogi reminds us. If you don't know where you're going, you might not get there."
Of course, the posting goes on to cite some sources, among which I find myself, for which I am gratified to be included:
 The Requirements Engineering Handbook, Ralph R. Young, Artech House, 2004 Requirements Engineering: A Good Practice Guide, Ian Sommerville and Pete Sawyer, John Wiley & Sons, 1997 Succeeding with Agile: Software Development Using Scrum, Mike Cohn Addison-Wesley, 2010. Project Management the Agile Way: Making it Work in the Enterprise, 2nd Edition, John C. Goodpasture, J. Ross, 2015. Agile Estimating and Planning, Mike Cohn, Prentice Hall, 2006 Agile Project Management for Government, Brian Wernham, Maitland & Strong, 2012.
What more on agile? Available now! The second edition .........
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