Success in Project Management (and the rest...) depends to a large extend to the Leadership of the PM and the sponsors. Such Leadership skills, or non-cognitive skills are typically recognized as the weak link of the chain. While whole libraries are available (and are probably re-published each year) on this topic, a few major elements are repeatably reccuring on this topic, as described below.

Attibutes of Leadership

In their Harvard Business Review Classic, available here Robert Tannenbaum and Warren H. Schmidt have identified 6 traits of leaders:
  1. - Energy and Drive: they are working hard, and get things done
  2. - they are willing to lead, and are perceived to constantly seek to inspire and influence with integrity.
  3. - they are assertive and have self-confidence
  4. - they have sound professional competencies, which enables them to take decisions and understand the consequences
  5. - they demonstrate intelligence 
  6. - they are open, communicate well, and extravertite

While the jury will stay out for ever on what exactly makes a great leader, the above is certainly a good set of references.

Watch this video (again from HBR) or this article for a slightly different  but compatible view, explaining that great leaders behave ethically, empower others, provide clear guidance, and communicate effectively

That there is no clear consensus about what is a leader, is probably due to the fact that there are many different types of leaders, each with a pattern of strength that make her/him more suitable to some missions or situations. In any case, leadership is multidimentional, and can be trained and developed. But this is a life long journey. Go there for a very good overview by Allan on the essential traits of a good leader, the ones that should be developed.  And more below as well...

Leadership: Trained or born?

he answer is: it depends. Professionals in this area tend to agree on the following:  

- 15 % of people may not need any training: they are natural leaders.

- 15% will not benefit from any training, because they are not willing to acquire the necessary behavior, or will not be able to.

- but for 70% of the population, and especially for those who need to lead in non-critical situations, leadership can be learned, through various tools starting from coaching program, 360degree assessments, and situational role-plays. In any case, this is certainly not the result of a one-week crash-course. 

What type of Leaders?

This article of the HBR presents various types of leaders. Each have their own attributes, and this is what makes them so-called situational leaders, because they will rather demonstrate their best in specific situations. The archetypes of the leaders:

  1. The strategist: leadership as a game of chess. These people are good at dealing with developments in the organization’s environment. They provide vision, strategic direction and outside-the-box thinking to create new organizational forms and generate future growth.
  2. The change-catalyst: leadership as a turnaround activity. These executives love messy situations. They are masters at re-engineering and creating new organizational ”blueprints.”
  3. The transactor: leadership as deal making. These executives are great dealmakers. Skilled at identifying and tackling new opportunities, they thrive on negotiations.
  4. The builder: leadership as an entrepreneurial activity. These executives dream of creating something and have the talent and determination to make their dream come true.
  5. The innovator: leadership as creative idea generation. These people are focused on the new. They possess a great capacity to solve extremely difficult problems.
  6. The processor: leadership as an exercise in efficiency. These executives like organizations to be smoothly running, well-oiled machines. They are very effective at setting up the structures and systems needed to support an organization’s objectives.
  7. The coach: leadership as a form of people development. These executives know how to get the best out of people, thus creating high performance cultures.
  8. The communicator: leadership as stage management. These executives are great influencers, and have a considerable impact on their surroundings.