In the group of words below which does not belong?

goal
objective
performance
potential
capacity

 The answer is Capacity

Explanation:

  If you are reaching fot something, some dream, some idea, you have a goal or objective. To reach it, you need to have a good performance a long your way untill get in your goal. Throughout your way about to achieve your objectives, you need to have a potential inside you. This potential is going to guide you through your ideas about the reaching your objectives.

 However, capacity isn't belonging about this four words listed. You may be able to achieve your goals, but that ability need not be intrinsic to you. Other people can help you achieve even without your ability to do so. That's the reason CAPACITY does not belong in this group of words.