According to psychologist Abraham Maslow, our needs can be generalized into several distinct categories and visualized as a pyramid with the most important and motivating needs at the bottom. Of course, our motivations may not exactly occur how Maslow theorizes it. Biological needs may not always win over other types of needs, though. This could be illustrated by starving artists who may prioritize buying expensive, but necessary art supplies over buying food, a basic necessity. Another example would be students who prioritize their need to accomplish in an exam over their need for rest. Despite these exceptions, in the end, our basic physiological and biological needs usually win out over the psychological, social, and self-fulfilling ones. 

From a personal perspective, our psych unit on motivation could not have been more timelier than this. Having contracted the flu over the weekend, I can see how my basic biological need for rest and recovery was an overpowering motivator over my cognitive need to work on school things. However, it is also worth noting that on top of exploring innate motivators, our psych professed added that "Even though it's 'normal,' it doesn't mean it's right." With that mindset, it's probably not best to tout some needs as an excuse to not do what you're supposed to. After all, excuses are like armpits; everybody has them and they all stink. :P