The way language teachers respond to learners’ failure to internalize language may considerably vary. Some teachers may prioritize making the language in their classrooms understood in its entirety, contrary to their teacher education in which roughly-tuned input is advised rather than finely-tuned input. Considering that teachers’ practices are often influenced by their cognitions, this study set out to uncover teacher cognitions on student understanding during their teacher education. The participants were 13 pre-service EFL teachers doing their practicum at high schools in Turkey. Participants were interviewed to reveal their cognitions on student understanding. Semi-structured interview tried to uncover how they coped with failure to understand when they were learners as well as when they observed how their mentor teachers handled learner failure to understand a linguistic feature or skill. The qualitative analysis of the interviews revealed that the pre-service teachers’ cognition on student understanding is a unified construct that covers many meanings of the word understand, and consists of pre-service teachers’ beliefs and pedagogic knowledge. These findings shed light on pre-service teacher cognitions, paving the way for education curriculum.