If IIT students despite being intelligent don’t do well in their career, is it because of their past life karma or present life karma?

From: Amit

We see that not all IIT students do well in life in spite of having good ranks, say within 500. Is this because of their karma due to past lives? Or is it because they pick up bad habits like smoking, drinking, pornography etc? Does this mean that they lose their good karma by indulging in their bad habits and lose their sharp intelligence to do well in life?