* Poor project specification
* Unrealistic timescales
* Timescales that are too long
* Inappropriate staff
* Insufficient involvement by senior management
* Failure to manage user expectations
* Failure to manage the change required

I would add “daily realities.” Faced with crises on current systems, end-users typically neglect responsibilities devoted to a new IT project. I mention a few other causes in my list but there’s a good deal of overlap between our two lists.