About prioritising in projects

What is most important? is the key to all priorities. In relation to the often complex relationships between Goals and Objectives I would just point out the following useful overview:
 

Input is a discussion about how much each success criteria means in the overall project. A valuable debate in itself! Then discuss how the desired functionalities actually is believed to contribute to the success criteria? Finally the multiplications gives an idea of the ​​importantce  of each functionality (Most for the buck) and of each delivery.
With this information, the project manager has a good (probably the best) background to prioritize what needs to be promoted and which can wait.