1. I think i'm one of the luckiest people in this world. say 'the world', because we know of only one world with people in it.
2. If you are on the top, you are afraid to fall, and if you are on the bottom, you are enthusiast to get to the top.
if you are at the top, you are afraid to fall; if you are at the bottom, you are enthusiastic to get to the top. (use the adjective 'enthusiastic', not the noun 'enthusiast'; actually words like 'anxious' and 'keen' sound better to me)