I'd not come across Cognitive Daily before - but they do a good job on presenting this research that shows that even bright kids would do well to work on their self-discipline if they want to really succeed.
Both IQ and self-discipline are correlated with GPA (USA: "Grade Point Average", an ongoing measure of academic performance), but self-discipline is a much more important contributor.
Those with low self-discipline have substantially lower grades than those with low IQs, and high-discipline students have much better grades than high-IQ students.
Even after adjusting for the student's grades during the first marking period of the year, students with higher self-discipline still had higher grades at the end of the year.
The same could not be said for IQ.
Further, the study found no correlation between IQ and self-discipline - these two traits varied independently.
Original research presented by Duckworth, A.L., & Seligman, M.E.P. (2005). "Self-discipline outdoes IQ in predicting academic performance of adolescents." Psychological Science, 16(12), 939-944.