“Getting ahead in a difficult profession requires avid faith in yourself. That is why some people with mediocre talent, but with great inner drive, go much further than people with vastly superior talent.” Sophia Loren
What this quote means is that it is your belief in yourself and your determination to succeed which gets you to your goal, rather than talent alone. Take two people, one with greater determination and who believes in himself and one with more talent, and the one who believes in himself will get further than the person with more talent.
The world is full of smart talented people who never reach their full potential, who die unknown and unfulfilled, never reaching their dreams. Then there are those with no talent whatsoever who reach the top through the sheer strength of their determination, and belief in themselves.
If you want something badly enough, a strong unwavering belief in yourself is what will get you there.