A quick article with opinions from six people on project killers: 6 Experts Share the #1 Thing That Derails a Project | Smartsheet. Of course, there are six different things listed as "the #1 thing." And there are a few more listed in the comments.
I mention this article because my friend, Johanna Rothman is quoted as suggesting multitasking is the killer, "The silent project killer, and in my experience the thing that kills more projects, is multitasking." Of course, I had to smile, seeing this. I often talk about this in my discussions of project management and Critical Chain Projects - specifically I talk about multitasking killing flow. Too much switching from task to task to task without getting anything done. This means we can't hand something to the next step in the line (without it getting stuck as well).
Please note: Having a queue of work is not multitasking. It's when I am forced to pull things into active mode before I finish what is in front of me.
A couple of the other suggestions in this article in my mind have to do with understanding what the project is. When there isn't alignment or agreement on what we are doing in a project, it almost guarantees that the project will get stuck in swirl and scope creep. Which often leads to even more multitasking as we try to figure out what it is that we are really supposed to be doing.