Trawl Requirements

Requirements are usually not gathered [Coh04]. Customers and business experts think they know precisely what they want. But when they see the end results, your team finds out that they wanted something completely different.

This is where the metaphor of gathering requirements does not hold. You could gather requirements if they would be lying obviously for everyone to pick and take away in order to produce the desired piece of software. Unfortunately, requirements do not lie around waiting to be picked up. Most teams have to learn this the hard way.

Mike Cohn suggests to use a different metaphor instead. Since requirements are not lying around waiting to be gathered together, we need to do something to get a hold of them. There are techniques that help you do that on different levels, just like a fishnet can have different netting sizes in order to catch different sorts of fish while letting others swim through. This analogy holds wonderfully for the different techniques of specification by example.