This phrase is used within the medical community to describe the process by which medical professionals in training learn and master various skills. The implication is that once someone can successfully teach another how to perform a procedure - from phlebotomy to intravenous line placement to the insertion of a urinary catheter to performing an appendectomy and beyond - he or she has mastered the skill.

This transfer of hands-on experience usually begins during the clinical years of medical school, where people further along in their training, such as interns and residents, demonstrate the execution of medical procedures to medical students. Generally, after seeing someone else perform a procedure a few times, a medical student might be given the opportunity to attempt it under supervision (sometimes, though, it’s just the student, the patient, and the needle for the first blood draw or IV placement). After successfully performing the procedure several times, the student might be called upon to teach it to someone else and supervise him or her in that first attempt. Fourth-year students teach third-year students; interns teach students and each other; residents teach students, interns, and each other while also learning from the attending physicians.

Some things just can’t be learned in a book, and if you see a few, do a whole lot, and then show someone else how to do it, you’re golden.