The primary thing when you take a sword in your hands is your intention to cut the enemy, whatever the means. Whenever you parry, hit, spring, strike or touch the enemy’s cutting sword, you must cut the enemy in the same movement. It is essential to attain this. If you think only of hitting, springing, striking or touching the enemy, you will not be able actually to cut him.
The McNamara fallacy, named for Robert McNamara, the US Secretary of Defense from 1961 to 1968, involves making a decision based solely on quantitative observations (or metrics) and ignoring all others. The reason given is often that these other observations cannot be proven.
The fallacy refers to McNamara's belief as to what led the United States to defeat in the Vietnam War—specifically, his quantification of success in the war (e.g., in terms of enemy body count), ignoring other variables.
In an empowered product team, the product manager is explicitly responsible for ensuring value and viability; the designer is responsible for ensuring usability; and the tech lead is responsible for ensuring feasibility. The team does this by truly collaborating in an intense, give and take, in order to discover a solution that work for all of us.
However, in a feature team, you still (hopefully) have a designer to ensure usability, and you have engineers to ensure feasibility, but, and this is critical to understand: the value and business viability are the responsibility of the stakeholder or executive that requested the feature on the roadmap.