Are most people determined to never achieve anything or improve at all?

Exactly how much do genetics determine how smart someone can be, or what they are capable of? What about environment? How come some people are capable of learning and taking things in with ease, and others will live their whole lives never being able to come close to that state of mind?

For example: if person A is naturally inclined to be good at math, and person B else isn't, will person B who wasn't good at math from the start or put in an environment that encouraged it ever be able to be as good at math as person A?

I'm trying to determine just how much people are in control of their lives, what their limits are biologically or psychologically. Just how good can someone be at something, and are some people just naturally wat better at something than anyone else ever could be? Is it true that only a select few people will ever accomplish amazing things, or is that all a matter of perspective and can just about anyone become anything if they set their mind to it?