It is widely assumed that the more experienced professionals become, the better (0) THEIR judgement will be in high-stakes situations. Research suggests, however, that this is by 1 means always the case. Experts can fall into what 2 known as 'the expertise trap' — the tendency to over-rely on familiar patterns and disregard contradictory evidence. 3 is this more apparent than in the field of medicine, where experienced clinicians have been shown to make diagnostic errors at rates comparable to those of 4 less seasoned colleagues. Not only does excessive confidence lead to mistakes, 5 it can also inhibit the collaborative thinking on which effective decision-making depends. Had researchers 6 aware sooner of how pervasive this problem was, the study of expert error might have begun decades earlier. Be that as it 7, the growing recognition that expertise can be a double-edged sword has prompted organisations to rethink the way 8 which senior professionals are trained and assessed.