This paper deals with the concept of falsification in hypothesis testing research. A theoretical analysis of assumptions about falsifying behaviour and hypothesis-falsifying observations is presented, with two experimental studies. Both the theoretical analysis and the experimental results point to a number of paradoxes underlying the normative principle of falsification in cognitive psychology. First, subjects experience the falsificatory testing strategy as an impossible strategy to conduct. Obtaining falsifying results is a consequence of the quality of the hypothesis rather than of specific testing behaviour (Experiment 1 and Experiment 2). Second, under some conditions falsifying results impede rather than facilitate discovery (Experiment 2). Confirmatory testing and falsificatory testing, which have been the crucial concepts in the study of hypothesis-testing behaviour, may actually be questionable approaches to testing behaviour. The theoretical analysis is related to the standard analyses of Popper (1963) and Klayman and Ha (1987). The empirical results are discussed in relation to previous studies on falsificatory testing behaviour.