"When I pass a series of inputs to the classifier, they are tagged with at least 65% precision and at least 65% recall." It could be that the available data an

"When I pass a series of inputs to the classifier, they are tagged with at least 65% precision and at least 65% recall." It could be that the available data and current approach yield only 63%, in which case the user story is being worked on indefinitely for months. Or it could be that 65% is achieved, but the threshold chosen was a wild guess; business value is actually linear all the way up to perfect, so it's worth iterating indefinitely. The scrum & user story format work well for small and unambiguous units of customer-facing behavior, but some software is made of more than that.