"If I believe in myself, I can do anything I set my mind to"-Why this saying is false

The saying "If I believe in myself, I can do anything that I set my mind to" I believe this is not at all true. People will tell you that I'm the one thats wrong and that you can do anything in the world as long as you try hard enough. The reason its not true is because God has a plan and opportunity for everybody that he has given us to do. For example, I suck at math. I find it hard and I will never understand it. God just didn't give me that skill in my life, but hes given me others to embrace and to embark on. I love to help people and God gave me the caring qualities that makes me love others and want to help. But I will never be a mathematician, chemist, or a bodybuilder and things like that. I will embrace what I can and can not do and I know that I and everyone can't do everything in the world no matter what.