It has always been challenging for designers and developers to readily pinpoint potentially viable opportunities for emerging technologies in people's daily lives. In ubiquitous computing in particular, the uncontrollable dynamics of a user's context makes this issue even more prominent. In this article, the authors assume they can't hypothesize what users of new technologies will desire. To address this challenge, they developed discovery-driven prototyping, which lets users control what they will do with new technologies. Here, the authors describe DDP and its effectiveness through a series of in- situ user studies.