As writers, we tend to fall in love with specific story ideas—teh ones that hit us in a flash, providing all sorts of energy, excitement, and inspiration. And in the beginning, when everything is shiny and new, those ideas often seem brilliant. Sometimes they are.
Be willing, however, to regularly and objectively evaluate how good your protagonist's story really is. Is it as absorbing and interesting as you'd hoped? If not, think about your secondary characters. Do any of their stories seem more interesting? Be willing to recognize the fact that there may be another character whose take is more worthy of being told.