Deke Sharon's excellent Total Vocal blog discusses the path from really good to excellent:
You cannot get better at performing by thinking about it. You cannot become a better singer by studying vocal pedagogy texts. [...] The problem is not a lack of goal, vision, or desire for excellence. The problem is an understanding of and persistence trudging through the marshes and the weeds. It's a long, difficult march, and while you're on the path, you not only know you're not great, you can likely hear your peers' low voices as they analyze your imperfections, just as you analyze others. And yourself. [...] Legends are made, not born. When you see Straight No Chaser or Pentatonix, you do not know the extreme effort behind their seemingly effortless rise into the public eye. Both have a work ethic that is second to none. They're proud of their success, but realize the elements of luck and timing, and do not take it for granted. You should not either. [...] There is no guarantee of excellent, but there is a guarantee of mediocrity. You must pass through the trials of self-doubt and question your own abilities. Perhaps for years.