The purpose of this study is to find out what kind of sources are behind student teacher self-efficacy based on student teachers’ own interpretations. A key starting point for the study of sources is Bandura’s social cognitive theory. It is important to know the content of these sources because self-efficacy has been found to be an important factor in the quality of teaching. A particularly noteworthy reason to study self-efficacy sources and their nature in teacher education is that the sources are in the process of being shaped and can be consciously influenced. The research participants were 25 student teachers in a Finnish teacher education context. Data were obtained through interviews, and were analysed using theoretical thematic analysis. The student teachers highly valued the experiences they had acquired themselves, and they were often linked to the emotions that strengthen them. For example, when a teacher notices that students are learning (even though there were difficulties at first), it brings pleasure to the teacher. Negative mastery experiences were sometimes associated with depression, but those negative experiences in the long run may also empower the teacher. Student teachers also made observations about other actors of teaching (and teacher education) and received comments from them. In practice, the source evaluation of those actors was hierarchical, with the supervising teacher and the school pupil being valued the most, and the peer teacher, i.e. the student teacher, being much less valued. The critical approach offered in teacher education and the general accompanying reflective “climate” in teaching practice will affect how feedback is – and should be – evaluated by a student teacher.