A success is a function of ability and opportunity i.e. Success = fn(ability,opportunity).
Having put the success in mathematical formula let us now try to understand it. Success depends on the ability that you possess and opportunity that is available to you. The absence of any of these will lead to no success.
Among ability and opportunity you have direct and permanent control over ability because you possess it. It is not dependent on any external factor. If you have it then you have it and if you don’t have it then you can at least try to acquire it. On the other hand, opportunity is something that is not in your control. One or many external factors impact the magnitude of opportunity.
So having ability in itself is nothing when denied opportunity.