The present paper argues for three reasons why knowledge's influence on ecological behavior is underestimated systematically. First, it is not the mere amount of knowledge available that determines behavior. Different forms of knowledge must work together in a convergent manner if they are to foster ecological behavior. Second, knowledge's effect remains undetected also, because some statistical procedures neither correct for measurement error attenuation nor uncover mediated influences accurately. Third, psychological factors such as knowledge apparently have a limited influence on ecological behavior when strong situational constraints are effective. When an ecological behavior measure makes-as a performance test-systematic use of situational influences though, knowledge can be revealed as affecting ecological behavior significantly.