Question

project management can be best described as a set of related activities which have a definite starting point and end state, which pursues a defined goal and used a definite set of resources with reference to this discuss the project life cycle, the qualities a project manager should possess and reasons for successful project management

As a graduate of Defense Systems Project Management School, I would be happy to critique your thinking. Remember that as the project ends, often some of the activities associated with the project are transfered to other life cycle managers, especially things like logistics, training, and upgrades. That transition is part of PM also.