Culture can be seen as the normative glue that holds an organization together. It is related to the institutionalized way of thinking and acting of people. Our aim is to study and characterize belief systems in software organizations. Our work highlights organizational culture influence by applying the Theory of Reasoned Action (TRA) to software project teams in terms of origins, sources and impacts of beliefs on software development practices. By applying TRA to guide two case studies, we were able to provide rich narrative accounts of software project teams, involving the influence factors associated to team belief systems and attitudes toward practice. Our research has gone through two cycles, comprising 2.5 years of study in Brazilian software companies. A particular moment of the research, the synthesis of the two case studies results is being explored in this paper. A set of interviews and observations was performed with professionals from different project teams and companies. A conceptual framework was built based on the TRA model to guide a cross-case analysis of the results. The synthesis of the analysis highlights the strong influence of past experiences and organizational contexts on software development practices.