Almost everyone can say they have experienced a time in their life when they wanted to do something but didn't believe they could - sometimes this negative belief becomes so strong that people fail to even attempt taking actions on their biggest dreams!
My question to you is, why do you look at someone and deem whatever quality they have that you desire is possible for them but impossible for yourself? Everyone does it but until we recognize that we are the only ones setting limits for ourselves, we can never achieve that thing that we want.
The biggest and best advice I can give, is the best advice my own coach gave me when I started competing fitness which was... to stop assuming your impossibilities and start keeping an open mind as to what is possible for you. Go after what you really want; set goals that may initially seem too high because when you set only small ones, you can only lead yourself to small outcomes, and a small life; but if you set big ones, you only open yourself to endless possibilities and living life in a big way!