I think they're born that way. I have two -- one is "self-driven" when it comes to school work and has been since day one of Kindergarten. He is also an introvert with a small circle of friends. My other one has to be nagged to do homework (on days he remembers to bring it home). He is very outgoing and has a huge social circle. He does do other things extremely well, like certain physical labor-type chores that my other DC needs to be nagged to do.
Focus on their strengths. I try to convince my school-slacker kid that no matter what he wants to be when he grows up, he has to do well in school first. I also accept that I have to be more deeply involved in his school experience than I would like to be. Sigh.
Mine are grown now, but I could have written this comment.
Here is one piece of advice: relax and do let the kid fail--not the big things, but the little things. (Not that I did this, but, hindsight.......) Also, try not to compare with the introverted self-starter.