One of the challenges in being a teacher is to set up an educational setting where the students receive relevant learning opportunities for the specific course, the students' education in general, and for their future. However, efforts to create such educational settings do not always work in the way that faculty has intended. In this paper we investigate one such effort seen from a critical incident perspective. Central to the analysis in this paper is how the Theory of Planned Behaviour (TPB) can provide explanations for the incident. The critical incident can be summarised as students refusing to take part in a non-compulsory, but from the faculty perspective highly educational, activity. We describe the incident in depth, give the background for the educational intervention, and analyse the incident from the perspective of TPB. This paper makes two major contributions to engineering education research. The first is the development of a method for analysing critical teaching and learning incidents using the TPB. The critical incident analysis illustrates how the method is used to analyse and reason about the students' behaviour. Another contribution is the development of a range of insights which deal with challenges raised by learning interventions, especially those involved with acquiring hidden or “invisible skills” not usually seen or acknowledged by students to belong to core subject area of a degree program.