" Enthusiasm makes the difference" Dr. Norman Vincent Peale 

i think this means that you need to have the spirit to do things. Like going to school, a sport, just doing anything you need to have spirit because then you will perform your best. For example, being enthusiastic can get you a lot of benefits because you won't be shy to ask for something. An example of being unenthusiastic is when you want something you won't have the courage to ask for it because you're shy or scared to ask for it.