“…Troublesome knowledge, in the lexicon of threshold concepts, is not simply knowledge that is difficult to understand, but knowledge that drastically alters one's perception of how that ‘piece of the world’ works. For example, ‘uncertainty in medicine’ emerges as a troublesome and transformative concept in the present study, as well as in other studies of medical students and palliative care physicians . Tolerance for ambiguity is considered essential for medical competence and yet some trainees enter medicine with the assumption that it is an exact science.…”