[luckydata]

It is definitely "ability to stay on task".

The difference between a great engineer and a mediocre one is the latter will just get distracted, stop working the problem and decide to go for good enough.

The great ones will work the problem, try multiple angles until something doesn't just work but offers the right balance of simplicity, elegance, future proofing and does the job well. You can't get there if every 5 minutes you take a facebook break, or can't grind through technical documentation and make experiments.

[newfoundglory]

Huh, I would probably include "the ability to stop at good enough" in my criteria for greatness. I've worked with people who couldn't resist looking for a better solution instead of checking in the one they had - even for time critical bug fixes.

[yeukhon]

This is one of the most objective views on "what makes a great software engineer" so far here. People who can focus generally deliver better work, even when they don't work on pet projects after work.