"Unfulfilled potential" refers to not reaching one's maximum abilities or talents, not achieving the success or progress that could have been possible. Full definition
Like Blanchett, Wiest gets Allen's juiciest female roles, playing a third wheel of unfulfilled potential in «Hannah.» (indiewire.com)
Meanwhile, the Catalan giants believe that the Danish footballer still has unfulfilled potential in his kitty unlike Coutinho or Ozil — both of whom they believe to have approached near to the peak of their individual abilities. (calcioinsider.com)
The «bigger Picture» is simply a lack of trophies and a lack unfulfilled potential. (justarsenal.com)