Thank you for the opportunity to help you with your question!
1) Poor communication across a team. In this case, no one knows exactly what must be done, and as such, different teams are working on increasingly different projects. In the end, poor communication creates a project that doesn't address the initial concern.
2) Insufficient QA. When a project is not given enough QA, or any QA at all, tech projects fail at an alarming rate. The project cannot address what it was designed to do, often because the initial project workers are unable to distance themselves properly to see the forest for the trees.
3) No clear goal. Big projects that are envisioned as solutions to emerging problems often suffer from a moving target syndrome. The project staff does not know what to work on or how to advance, and project managers must make constant changes.
Please let me know if you need any clarification. I'm always happy to answer your questions.