Put another way, the incentive for one organization is a date, for another it's features, and for the third it's quality/stability. I don't know who this "truth" thing is referring to.

All three of those incentives are negotiable depending on the circumstances and ultimate goal of the project. Some projects are necessarily date-driven, eg "If we miss Christmas we might as well cancel the whole thing". Others are necessarily feature-driven, eg. "If we can't provide all the table stakes features then we look like idiots." And others are necessarily quality-driven, eg. "If the thing crashes we'll lose the entire crew and the country will hate us forever."

The trick is to figure out what you're ultimately optimizing for. Once you've firmly established the *primary* objective, then you can start the important horse-trading that smoothes your triangle into a circle.

That's the meeting where you realize that if you move the date out by 10 days you can accommodate feature X which happens to be THE feature that really makes the whole thing sing and that somehow helps stabilize the entire endeavor.

Your metaphor of a triangle implies that these roles and arguments have sharp, pointy edges when with the right attitude, leadership and diplomacy, they can be sanded down to a virtuous and productive cycle that works in service of the project and the team.