Agile ideals and practices are enhanced by psychological safety, according to studies, and some practitioners have even said that "agile doesn't work without psychological safety." However, its origins have not been studied by academics. In this research, we aimed to comprehend the manifestation of psychological safety in agile software development teams. An exploratory qualitative phase (18 interviews) is followed by a quantitative phase (survey research, N = 365) to widen the empirical coverage and evaluate phase one's results in this two-phase mixed-methods study. Our research demonstrates that when people, the team, and the leadership embrace and promote practices helpful to fostering a psychologically safe workplace, psychological safety is achieved in agile software teams. While transparency and a lack of blame for team members are the "butter and bread" of psychological safety, team decision-making as a whole and leadership ownership continue to be its cornerstones. Slack time, technological techniques that operate as a safety net, and team autonomy, on the other hand, were not found to support psychological safety. This replication package includes the files and data needed to distribute our study's findings and analyses.