You don't get what you deserve -- you get what you negotiate.
That's an axiom of professional negotiators, and it's true in spades for project managers. The art/science of project management is overstuffed with formulas for just about everything, but none of it works without the wise management of the relationships among the stakeholders.
Any relationship is a constant two-way stream of requests, promises and value exchanges, large and small. With projects, it is vital that, from the very beginning, all the stakeholders are clear on what this is all about, including what their contributions are to be.
When projects fail, there always is some measure of short-circuit in the examination of assumptions, the communication of expectations and the settlement of differences. Those are the components of negotiating strategy. More noticeable are shortfalls in status reporting, problem-solving, schedule management, etc. -- the tactics of negotiating -- which can be either symptoms of strategic issues or sources of independently occurring problems.
As a project manager, you are the catalytic agent among the stakeholders, beginning with the owner/funder, through both close and remote contributors and on to the end user/customer. You are the keeper of the communication, the lead negotiator.
Troubled projects of my experience generally have a sizeable set of unexamined or unshared assumptions, leading immediately and inevitably to diverse expectations among different stakeholders and the resulting conflict that just keeps coming no matter what the project leadership attempts to do to resolve it.
The competent project manager understands that the very basis of a healthy project is thorough, shared understanding. Everyone involved must work out agreements as to the reasons for the project, the pertinent realities of the situation that gave rise to it, the priorities for action, and risks and assumptions that will affect the planning process.
Where there are differences among stakeholders, they must be exposed and cleared up so the process is founded upon solid consensus. Without that fundamental negotiation, the project will be beset with problems.
It isn't particularly easy to get the stakeholders to focus on this initial process and accept ownership. The project manager must get it done, but it's only the beginning. During the execution of the project, it's a continuous requirement. The work often entails finding ways to solve problems that shouldn't be occurring and re-energizing motivation where it shouldn't be slipping. Bummer.
Just getting a complex project done is demanding enough in itself. The project manager shouldn't also have to be constantly negotiating to keep things on track. Project managers deserve better. They're just not going to get it without negotiating.