There is lots of discussion of the number of projects that fail. Standish has their "infamous" report with all it's faulty statistics. But there is a better set of data in a broader domain. "The core problem of project failure," by T. Perkins., 2006, The Journal of Defense Software Engineering. Vol. 3, 11, p. 17. June 2006.
Of 155 failed software projects, Perkins tells us for each of the 155 project
- In 115 project managers did not know what to do
- Of those 115, 110 had not received the proper training
- 105 project managers did not have the proper experience
- 120 project management overlooked the need to implement a a project management principle
- Of those, 110 did not properly their knowledge
- 125 allows constraints to be imposed from higher levels that prevented them doing what they know they should have done.
- Of those, 110 did not properly their knowledge
- 130 did not believe formal project management principle added any value.
- 135 believed that project management were flawed.
- 140 thought the Project Manager's goal was something other than the success of the project.
- 145 said policies and procedures prevented them from doing what they knew they should be doing.
- 150 said statutes prevented them from doing what they knew they should do.
Notice a trend here. It's the project management skill, experience, processes, and support that is a root cause of project failure. Others have stated other causes, like requirements, stakeholders, technology, and other topics.
These are second order items. Notice that each of the 8 areas include those items.