During a product development process, decisions constantly have to be made. The success of the development therefore heavily depends on the quality of the decisions taken. Every decision itself is mainly influenced by two factors. On the one hand, it is the availability of system-relevant information and to what extend that information is reliable. On the other hand, the humans, and accordingly their, e.g., experience, emotional state, and knowledge, who are responsible for making the decision play an important role. To support the decision-making process, this chapter focuses on the non-visible aspects, namely, the inner processes of humans, which determine the outcome of a decision. In that context a model is presented which visualizes the process of believing while a decision is about to be made.