During new venture creation, entrepreneurs make decisions in a variety of areas from seeking funding to hiring employees. When and why entrepreneurs use effectual or causal logics to make such decisions is poorly understood. In this study, we integrate ecological rationality theory and effectuation theory to examine how the nature of decisions influences entrepreneurs' use of decision logics. In a qualitative study with 41 entrepreneurs across 290 decisions, we explore how decision content (what the decision is about) and decision structure (what information about a decision is represented in the decision-maker's mind) influence entrepreneurs' use of effectual or causal logics. We extend our findings in an experiment with 224 entrepreneurs where we manipulate decision structure. Our results suggest that decision content influences entrepreneurs' mental representations of decision structure. In turn, the combination of two elements of decision structure — decision complexity and the perceived costs of implementing different options — drives entrepreneurs' use of decision logics. We contribute to the effectuation literature by integrating it with ecological rationality theory, introducing the concept of decision fit as a driver of decision logics, and developing our understanding of hybrid decision-making (the simultaneous use of effectuation and causation).