Recent developments within the field of innovation management have stressed the influence of emotions during idea development. This is important since emotions influence the way people act, and when it comes to ideas, emotions may even constitute the driving force that propels the development of an idea forward. This paper aims to add to this research trajectory by focusing on the emotional aspects in idea development. More specifically, this paper investigates the research question: How do belief and associated biases influence idea development? To empirically explore this topic, data from five different R&D project teams engaged in idea development activities was collected via semi-structured interviews. Results from the study show that numerous biases exist in the vicinity of idea development activities. Further, the identified biases were in many cases influenced in opposing ways (i.e., either favoring or opposing the development of an idea). Finally, biases pertained to three different areas with the result that three distinct tensions were identified. The first tension, denoted the “Positive Illusions” Tension, relates to the belief in the idea and resulting framing issues. This tension also appears to be particularly tricky since it includes a self-reinforcing component. The second tension—the Newness Tension—concerns the newness of the idea and a struggle between escalation of commitment and self-preservation mechanisms. The final tension—the Ownership Tension—relates to the perceived ownership of the idea, and how it can shift over time. Ultimately, the presence of belief and associated biases in idea development seems inevitable. However, the influence they have appears to be a balancing act between removing biases and maintaining the motivation of the actors involved. Managing this balancing act appears to be particularly important when it involves ideas that are creative or uncomfortable, i.e., in innovative situations. Managers are encouraged to make use of an outside perspective, pay special attention to ideas that fit into the tension areas identified, avoid an overly strong reality check for immature ideas, and finally “boost” the development of those ideas that risk too little attention from the team.