Does desire solely drive behavior?

The week before Mardi Gras break, we were actively discussing Hume and his work titled: From Rationalism to Empiricism. Hume held that desires and emotions ultimately govern human behavior, not reason. Coming to think of it, I don’t necessarily agree with Hume’s claim. Because I, for one, know for a fact that I don’t complete my school work out of pure desire. I complete my assignments simply because they are mandatory and required in order to pass and ultimately achieve academic success. I reason with myself that if I don’t complete my work; I will have to face consequences. Now I know the example I provided is a very basic one, but unless I’m completely misinterpreting Hume, I’ve made my point. And I believe there are many other simplistic examples that contradict Hume’s viewpoint. Now all of this begs to question just how Hume exactly defines desire.