So, let's say you wanted to become the best at something. You train, and work hard everyday. Then one day you are the best. But where is there to go once you reach the top? "There's nowhere to go but down," Right? Wrong. You can't center all your hopes and dreams on one item. If you put all your eggs in one basket it will become a really heavy basket. It will burden you and cripple you.
That's not to say you shouldn't try. You should definitely try, just not kill yourself. Fear of failure and fear of mediocracy kind of go hand in hand. If you don't believe you will accomplish your goal then you either believe that you will fail or do a poor job. Fear is all consuming. It grabs ahold of your heart and your brain. It makes you think irrationally.
In my experience fear of failure leads straight to anxiety. When I believe with my whole being that I'm going to royally screw up I overthink. And when I overthink I grow super anxious. Sometimes leading to full on panic attacks.