Super Mario is a metaphor for Mario the plumber defeating his inner demons to become the best man he can be. No one told him he should face an army of malevolent mushrooms and angry human-sized turtles but he does it anyway in order to rescue the woman he views as his princess. Mario the ideal man does not give up when he is told his princess is another castle. He does not give up when he is presented with new obstacle after obstacle be they pits of nothingness or sharp spikes. Finally, he overcomes all of this to face a fire breathing villain who will ultimately fall to his determined mindset and superior force of will. This is what makes Mario more then just a mere human, it is what makes him "Super".
Source: