Test the prototype with real live humans, and validate. The team finally gets to see live users interact with their idea,s and hear direct feedback from the target audience. Everyone on the team observes the Validation sessions: watching your users try out the prototype is the best way to discover major issues with your design, which in turn lets you start iterating immediately. In addition, the team can organize a review to collect feedback from Technical Experts or Leadership Stakeholders.
It is important to note that the five phases, stages, or modes are not always sequential. They do not have to follow any specific order and can often occur in parallel and repeat iteratively. Given that, you should not understand the phases as a hierarchal or step-by-step process. Instead, you should look at it as an overview of the modes or phases that contribute to an innovative project, rather than sequential steps.

“Sprints begin with a big challenge, an excellent team — and not much else. By Friday of your sprint week, you’ve created promising solutions, chosen the best, and built a realistic prototype. That alone would make for an impressively productive week. But Friday, you’ll take it one step further as you interview customers and learn by watching them react to your prototype. This test makes the entire sprint worthwhile: At the end of the day you’ll know how far you have to go, and you’ll know just what to do next.”