Output is easy to measure: tasks completed, features shipped, documents written. Measuring output rewards movement over progress. You can satisfy every item on a task list while having no real impact on the thing that matters. Outcome requires knowing whether the work changed anything, which is a harder question and one that often doesn’t get asked until after the work is done and the result disappoints.
Solve the problem not the feature is the upstream version of this, if you start with the outcome you’re trying to change, the feature becomes a means, not a goal.