Ability
Ability should be considered a hidden talent until seen. Ability needs evidence to be recognized and judged.
What I mean by this is that we estimate or imagine that a person might have a certain ability given his background, education, interests, and even his home life. We can't say what his performance would be in the particular task in question.
Ability depends on the visual performance of a job.
When we see a person at work performing a specific task, we can judge or estimate his ability to perform that particular task. His ability to perform an unrelated task can only be evaluated partially on how the other job was completed.
A person may perform acceptably doing one task - showing he can do that task. What cannot be determined is how well he will do in other positions doing its required tasks. Since we have not seen him in action, we do not know his ability to do the work necessary for the functions in this new position.
Many individuals may be assigned a particular job or given a specific role but may not be able to perform what is necessary for that position.
He may not have the ability for the role as he has yet to be seen doing the required tasks.