If your parents are rich and have are around and can provide excellent schools, nutrition, love and care, pay for extra-curricular activities etc, you are far more likely to end up being "smart" and "have discipline" than someone who grows up in a family where parents are absent, they have to go to an inner city school, they can't afford school trips, instruments, extra-curricular activities, since they have to have a part time job themselves to make ends meet.
My point is, that SO many of the qualities we think that somehow kids got "innately" are actually purely products of luck and circumstance. The ability to "work hard" isn't a gift some are born with and some are born without, it's learned and modeled from our lives, parents, teachers, experiences etc.
If you never have parents that buy you books and encourage you to read, it's doubtful you will end up being "smart"