While managing projects, PMs need to efficiently collaborate, negotiate, engage, lead, cooperate with others. Thus it is crucial for a PM to be able to efficiently and constructively perform these skills. And what is not less important, we need to be able to proactively resolve possible issues and conflicts.
Meaning, the work of a Project Manager should facilitate the project delivery process, not interfere it. The key criteria is a capability to communicate effectively and to lead others. PMs should be easy-going, engaging, reliable, motivational, flexible, proactive, be able to negotiate and meet the consensus. We need to make people want to work on the project, to participate and to contribute to the best possible outcome.