The importance of putting 'who' before 'what' means choosing the right people for the right roles within the project team.
This cannot be underestimated.
Research in Jim Collin's book, 'Good to Great' confirms unequivocally that hiring the best people first, often before the exact roles are defined, and allowing them to set out the plan and direction was a secret to these companies' success.
Remember this when choosing your project team - it is not ok for the organisation to allocate people to your project who are not 'fitting in' or successful in other pats of the organisation first.