Self-discipline better than IQ in achievement

David Munger, a research blogger who reports on cognitive research, has a recent article, "High IQ: Not as Good for You as You Thought", which reports on research by Angela Duckworth and Martin Seligman that shows that self-discipline is much more important than IQ in academic achievement. According to the study,

Most impressive was the whopping .67 correlation between self-discipline and final GPA, compared to a .32 correlation for IQ.

In other words, practice makes perfect, and the more one practices, the more perfect one becames.

That makes sense. We wouldn't expect an Olympic athlete to not put in lots of hours of practice and work-outs if s/he wanted to win a gold medal. Why would anyone think differently about academic achievement?