The effect of self-control on individual behavior has long been a subject of debate. The psychology literature has advanced three theories to explain self-control. However, those theories carry contradictory predictions as they were restricted to linear relationships between an initial act of self-control and subsequent self-control ability. This study uses biometric measures collected in a random assignment experiment to look at possible non-linear effects. This was done by considering the variation in the effect of an initial self-control task on purchasing decisions as compliance rates with the task change. There is strong evidence pointing towards the conclusion that the self-control theories are not mutually exclusive and are actually operating simultaneously. Specifically, moderate self-control exertion in the initial task was tied to the knowledge structure and higher self-control ability in subsequent purchasing decisions. On the other hand, exerting self-control beyond a certain threshold caused a fatigue effect, which made the resource depletion models more dominant and resulted in lower self-control ability in subsequent purchasing tasks. This result was robust across several model specifications. Moreover, data from brain activation capturing approach behavior in the prefrontal cortex conformed to those findings. Finally, it seems that males were not only able to access the knowledge structure more quickly than females, but they also had higher fatigue thresholds and were able to withstand higher levels of self-control in the initial task before resource depletion became dominant.