A doctor with good critical thinking skills will intervene when required, but abstain from intervening wherever possible. He or she has the ability to apply resource stewardship, acknowledges the limitations of guidelines and is able to deviate from protocols when appropriate, with sound arguments for why this is in the patient's best interest. We believe that critical thinking is an important skill for any doctor, and that it will contribute to better patient-centred outcomes at lower societal costs and with greater job satisfaction among healthcare professionals. The current medical curriculum for medical students and doctors in specialty training in the Netherlands highlights several aspects (e.g. evidence-based medicine, shared decision making, cost awareness) that are required if the student is to become a critically thinking doctor. This focus should, however, be further emphasized, and should include knowledge of cognitive bias and the skills required for the critical thinking process. On the basis of three patient vignettes several forms of cognitive bias are described, along with bias-mitigation strategies.