This study was designed to understand the everyday experiences influencing the self-efficacy of a group of engineering students preparing for the TECO Green Tech International Contest. It also aimed to understand whether participants’ self-efficacy levels fluctuated under the influences of these experiences. The paper takes a qualitative approach using focus group discussion, journaling, and one-to-one interviews as data gathering tools. Our study confirms previous theoretical assumptions and empirical findings that four sources of self-efficacy information are related to self-efficacy beliefs. In addition, the study also supports the role of collective efficacy and context in influencing engineering students’ self-efficacy. During the first two weeks of the contest preparation period, participating students experienced a low sense of self-efficacy under the influence of perceived lack of knowledge and skills, contest pressure, doubt of team ability, and negative feelings. A couple of weeks prior to the contest, as the students draw inspiration from a growth in knowledge and skills, verbal feedback, and positive feelings, their self-efficacy was enhanced. Comparison with team members and trust in the advisor’s credibility also strengthened their sense of self-efficacy. This research has the potential to inform the development of engineering undergraduates’ contest self-efficacy.