Most sectors of industry, commerce and government have reported variation in the performance payoff from electronic customer relationship management (eCRM). In this paper we build on a surprisingly sparse literature regarding the importance of managerial discretion, to show that the heterogeneity of beliefs held by managers about eCRM execution matter when explaining eCRM success. Drawing on a data sample comprising 50 interviews and 293 survey responses we utilise segmentation techniques to identify significant differences in managerial beliefs and then associate these belief segments with eCRM performance. Results indicate that (1) three distinct types of managers can be identified based on the heterogeneity of their eCRM beliefs: mindfully optimistic, mindfully realistic, and mindfully pessimistic. (2) Further, our results imply that there is far less homogeneity at the individual firm level than is normally assumed in the literature and that (3) heterogeneity in managerial beliefs is systematically associated with organisational performance. Finally, (4) these results serve to remind practitioners that eCRM performance is dependent upon the right balance between managerial optimism and realism.