Through the years, I have had many conversations on the topic of why projects fail. One of the best lists I've come across is from the UK OGC Best Practices site - with some slight edits for non-governmental domains.
Inadequate linkage the broader community’s key strategic priorities and measures of success.
Insufficient involvement by stakeholders
Ineffective engagement with stakeholders.
Limited experience with dynamics in endeavor
Inadequate attention on goal elaboration and refinement into manageable execution steps and constraints
Evaluations driven by short term focus rather than long-term value
Ineffective communications between consumers and suppliers of technology
Ineffective issue triage across responsible agents