1. Lack of Project Clarity
Clearly if no one else understands the project being worked on, it is going to be hard to get everyone moving in the right direction. And yet, this is a top reason why projects get killed or slowly disappear.
How can you overcome this? As a start, write down a definition of what the project is, an ideal customer for the project, and what the project solves for that ideal customer's problem.
Once it is written down, it becomes less ethereal and a sort of first vetting of the project. It also tests how others understand the project from the perspective of both the project team as well as for the potential customer.