Shared decision making can help patients feel supported and empowered when deciding between healthcare options. Decision regret can be a meaningful measure of the quality of that encounter. However, in a patient-engaged research study examining shared decision making for breast cancer surgery, decision regret was a difficult construct to assess, and asking questions about decision regret caused the patient to experience that emotion upon reflection. In this article, we consider the complexity of decision regret, and discuss the difficulty of measuring that emotion through existing instruments. We call for clarity in definitions of decision regret and offer suggestions for developing a set of questions that can capture regret in a more meaningful way.