Most people can't be what they want to be...
Most people can't be what they want to be because they don't *know* what they want to be.
What a strange design: a creature born not knowing what it was born to be. So it drifts through life reactively rather than proactively.
I know what I want to be, but it took a freakin' *tremendous* amount of time and introspection and hard thinking to figure it out. I guess most people who know what they want to be found out through luck: they were doing something and they suddenly realized "This is what I want to do with my life." Jodie Foster is a great example of that kind of person.
Hope this helped!