The study identified factors that make an evaluation of decision-making capacity (DMC) difficult for clinicians in their daily work. Semistructured interviews were carried out with 24 healthcare professionals from Switzerland and subsequently thematically analyzed. The challenges they faced when evaluating DMC stemmed from three main concerns: patient characteristics that impede DMC evaluation; differing opinions and consequences of DMC evaluation; and familial and legal situations that complicate such evaluations. Physicians must be adequately trained to evaluate DMC as it is closely related to basic ethical principles of respect for patients’ autonomy and beneficence. Extensive training on DMC evaluation and the legal concept of capacity should be part of pre- and postgraduate education.