Six teams from six countries had three days to answer one brief: cut CO2e emissions from urban mobility by 20% in two years, in a world where changing how people commute is a behaviour problem, not a technology one.

The sprint's facilitator put me forward as Decider, the design-sprint role that sets the criteria for a decision and breaks ties when the team can't agree, given my MSc research in smart cities and mobility, my own reading on behaviour-change design, and hands-on gamification experience from TobyRich. Five people, most of us meeting for the first time that morning: a UI/interaction designer, a visual designer, two from sales, one full-stack developer. My scope ran end to end, problem statement, persona, concept direction, prototyping, and the pitch itself, all while keeping five strangers moving toward one decision with a clock running.