Open source software communities have demonstrated that they can produce high quality results. The overall success of peer code review, commonly used in open source projects, has likely contributed strongly to this success. Code review is an emotionally loaded practice, with public exposure of reputation and ample opportunities for conflict. We set off to ask why does code review work for open source communities, despite this inherent challenge. We interviewed 21 open source contributors from four communities and participated in meetings of ROS community devoted to implementation of the code review process. It appears that the hacker ethics is a key reason behind the success of code review in FOSS communities. It is built around the ethic of passion and the ethic of caring. Furthermore, we observed that tasks of code review are performed with strong intrinsic motivation, supported by interestingly many non-material extrinsic motivation mechanisms, such as desire to learn, to grow reputation, or to improve one’s positioning on the job market. In the paper, we describe the study design, analyzed the collected data and formulate about 20 proposals how what we know about hacker ethics and human and social aspects of code review, could be exploited to improve the effectiveness of the practice in software projects.