Lack of Goal and motivation!
Talent is useless if not put into good use and only relies on nothing else to succeed. One could have a talent in singing but never ever sings in public just because he/she deems it unneccesary.
If one likes to succeed with their talent, one must go out and show the world what they can do. They must have a clear goal in place and the motivation to pursue that goal. Going back to the singing part, one could join talent audition contests and the likes to showcase their talent. Plus with the invention of technology and social media, one could just record it and put it up on Youtube.