Agile works because it is designed to help teams adapt to changes in direction. Agile is designed to minimize the pain of changing requirements. Agile proponents believe the premise that requirements will change and no amount of upfront planning will impact that. They believe that the requirements simply do not exist until after something has been built. Agile processes save a lot of time by not doing big upfront requirements gathering or design work. They also don’t involve big up-front planning. They do small planning work. And they do it again and again, throughout the project. This works because they minimize wasted planning effort.