There is somewhat of a zero-sum game between our intellect and our emotions. The brain depends on energy, just like a car depends on gas. If too much fuel is going to our pre-frontal cortex to support cognition, less fuel is available to the parts of the frontal lobe that inhibit our emotional impulses. This was shown in a 1999 experiment by Baba Shiv and Alexander Fedorikhin. Subjects were given two different memory tasks, an easy task (to remember two digits) and a difficult task (to remember seven digits). Remember we can only hold about seven digits in mind at a time. Subjects were then offered their choice of either chocolate cake or a healthy fruit salad. People with the easy task were more likely to take the healthy food while people with the difficult task were more likely to take the chocolate cake. The authors interpreted this to mean that energy expended to perform the harder memory task depleted the brain’s ability to resist temptation.