Prioritization can not only be ruined by the lack of a system. Dangers to proper decision-making are within the team: the opinion of the leader or overly expert opinions you can't argue with, or spontaneous decisions based on client requests. Find out some common management mistakes to avoid them in your team.
Really High-value New Opportunity—a sales-person with a customer deal for an unplanned feature insisting re-allocating resources to build what's required to win the deal.