There is nothing more certain and unchanging than uncertainty and change. John Fitzgerald Kennedy I would like to use this opportunity to share with you my reflections upon the privileges and the challenges of a decade of teaching of teaching medical students. I’ll describe how my clinical practice in the field of emergency medicine informs my teaching sessions and why I believe a good understanding of physiological systems is vital for safe and effective patient care. I’ll also tell you about the fatal consequences of a doctor that didn’t appreciate that the QRS complex of the electrocardiogram is due to ventricular depolarization and the misconceptions of a diabetes specialist who thought that osmotic diuresis caused glycosuria.