You should read an excellent post by Mike Kavis on The Virtualization Practice about the many common reasons behind Agile initiative failues. These mistakes are usually the death knell of DevOps initiatives as well.
Some of the sure-fire ways to kill an Agile initiative include
- Constantly changing priorities
- Not including all of the non-IT departments in the initiative as well.
- Unplanned work
- Bypassing architecture planning sprints