What single quality predicts a good doctor? Curiousity. (blogs.scientificamerican.com)

I think it's also likely that curiosity correlates with being a good hacker:

- Is there a better way to do this: Another language? Another algorithm?

- What's the real cause of this bug?

- Has someone already solved this problem?

- What problems are my co-workers working on?

- What does that unfamiliar bit of syntax do?