For example, creating a common vision of success is key. As you do this you will find that new requirements or redefinition of existing requirements will occur, and that affects both scope and estimates.

Below are links to two relevant white papers that I wrote on Earned Value Management a few years ago. They discuss scope management and estimating - two things that are essential to project success.

http://comp-soln.com/EVM_scope.pdf
http://comp-soln.com/EVM_estimating.pdf

There are certainly many other reasons that projects fail, but getting a solid start to a project will minimize the chances of failure. And, using EVM on an ongoing basis will help identify problems early-on, giving you time to make corrections early before things get out of hand.

Cheers,

Chip