The experience of earning an engineering degree can be hard to understand. All through undergraduate and graduate training, students are handed a steady stream of increasingly hard puzzles. Classes introduce new tricks to solve these puzzles, each with a correct answer and an accepted solution. Students develop a professional identity as being very effective at solving puzzles--no matter how challenging, no matter how morally tricky. Failing to solve a puzzle feels like a personal failure. This enthusiasm for problem-solving, though, needs to be balanced with a critical perspective that draws from social sciences and the liberal arts to focus on the humans who will be affected by technology. To avoid building tools that do more harm than good, science, technology, engineering, and math (STEM) educators need to expand their pedagogies and teach that saying "no" is a valid option. This article presents why these educators need to teach design refusal.