Software development is complex. We might think we know upfront what the final product will look like. The graphic designers put hard work providing the mock-ups and even a prototype on Sketch or Adobe AD. Maybe you hired developers telling them that you wanted pixel-perfect development. The story map is precisely defined. Everything is ready for a few development cycles. What could go wrong?
Remember that in any project, and with any new product, there are the things that you know, the ones that you know you don’t know and the ones that you don’t know that you don’t know. So you have to be prepared to re-negotiate the scope at any time. What tools do you have to do so efficiently? Impact Mapping is a great one.