Researchers have extensively studied how entrepreneurs use heuristics. We explore how the various heuristics that have been articulated may have a different effect on causal than on effectual entrepreneurship. Based on the distinctions between the two approaches, the paper outlines five pairs of heuristics that may affect the approach chosen and its effectiveness. We conclude that, paradoxically, people may have a proclivity towards the approach by which they are most likely to fail. This suggests that, to be successful, entrepreneurs would need to step beyond their natural preference for a particular approach or to develop ways to cope with their biases.