Because Every program at DARPA is intensely technically scrutinized by the tech council the framework (as I have interpreted it) is “be able to explain precisely why this idea will work to a group of really smart experts both in the area of the program and adjacent to it.”
The amount of risk the council is willing to take on depends heavily on the office. The Defense Science Office - DSO is much more risk tolerance than the Tactical Technology Office - TTO that actually builds prototypes and passes them off to the military.
PMs get informal feedback throughout the process on whether the program is likely to be approved by the council. It’s key that this feedback is from people who are good models of the council as opposed to schmucks with an opinion, which is the case in many other areas. I suspect there is something important about this zero-consequence but tight feedback loop during the design process.
The unstructured framework depends on DARPA PMs being extremely smart and self motivated because there is almost no explicit guidance and the feedback loop depends on self-motivation. The best DARPA program managers are the ones who can look at an entire literature in an area and notice a systemic bias. But at the same time it does give them a very fixed end goal - answering The Heilmeier Catechism. Although note that the Catechism wasn’t created until after DARPA had many of its early wins.
The unstructured nature of the framework may be one reason that The dependence of DARPA on high quality program managers mirrors the obsession with “talent” in other disciplines.