In the words of legendary usability pioneer Jakob Nielsen:
"The first rule of usability is: never listen to what users say. Watch what they actually do."
Human beings are notoriously poor at predicting their own future behavior. In focus groups or surveys, people claim they would love a feature; when put in front of the actual software, they struggle to find it.
Usability testing is not an opinion survey; it is a scientific observation of human interaction with a product.
Level 6 · Workflows and Deliverables