Most places you look will give you reasons with percentages. A key item is to be able to demonstrate that if one keeps doing the same thing over and over, the results will be the same. If you do not change the input, the outcome will always be the same. If you do not have a committed sponsor, the project will fail (success being defined as a quality product being delivered on time and within budget). I'd suggest you take a look at 'Anti Patterns, Refactoring Software, Architectures, and Projects in Crisis', by William J. Brown et all, ISBN 0471197130. The book outlines several patterns of activity that lead to project failure and methods to correct the issues. You must get your team, from top to bottom, to recognize the difference between participation and commitment, e.g. in a breakfast of ham and eggs the chicken is participating and the pig is committed.