If one is to assume a changing role for rationalization in contemporary collectives, how may we consider the relationship between expertise and professionalism? It can be affected by three challenges: maintaining the classical domination of experts; trying to cope with counter-expertise and conflict; organizing participative expertise. The outputs of these situations are influenced by an identical factor: the paradoxical importance of misunderstanding, which relies on the weak implementation of the strong equipment, patiently elaborated. The first case is examined with a limited approach of this general perspective: experts in medicine and dentistry who try to rationalize their colleagues' practices via guidelines, may be considered as specimen of the classical exercise; members of a symphonic orchestra who cooperate with pupils in specific projects with the help of professors and animators, may portray the aim for participative situations. These situations appear to be open to mutual evolutions.