That's not to downplay the impact of weak relationships, poor communications, and distrust. Those are biggies, to be sure. But it seems to me that the way we define the goal has a big impact on our decision making and our eventual outcomes.
See, even with great trust and communication, if we head in the wrong direction we're going to end up in the wrong place. If we think adding a hundred new features, extending the schedule by 10 years and increasing the budget by billions is going to make the product better, um, we're going to end up with stuff that's bloated, broken, operationally irrelevant and technically obsolete.
That's why the focus of FIST is on the program's values - the statements of preference and priority, the definitions of goodness which define our objectives. FIST says it's important and good to be fast, inexpensive, simple and tiny. And there's a lot of data that suggests simple, low-cost systems out perform complex, high-cost systems. When you're aiming for a quick, inexpensive solution, you're more likely to build good relationships, communication, etc, because such solutions are more human-scale. You're more connected & invested in them than if you were on a thousand-person team half-way through a 20-year project.
But when we think it's important and good to spend a lot of time and money, developing a hugely complex system, we're going to end up going in the wrong direction. Trust and good communication are important, but they might not help with that sort of problem.