Passion for Learning

What causes a passion for learning? What causes that spark in one's mind that builds a fire that can only be quenched with knowledge? We have talked about how one needs a passion for education, or what they are learning to really retain the information. It is also important to note that there is a difference between retaining information and really learning, as opposed to memorizing something that you will use for a short amount of time, and then when you have finished with the information, you forget it. What causes a passion for learning? If you don't have a passion for learning, why continue your education?