I just got yelled at in a Comment by Brad on a recent post.  In my answer I pointed him to an older post on GSD, because I am serious about the mental habits and growth of my team in general.  In support of GSD, a removal of any "language tunnel vision" is something of a necessity.

When we're recruiting, we look for a willingness to try new things more than what people actually know. We're doing that now, so I've been thinking about this a lot.

The GSD links back to another old post, in which I state, equally seriously, that consistent and disciplined use of a developer tool or tools is no guarantee of productivity.

But what is?  Developers have to have logical minds, sure.  What else, as personal characteristics?

• an ability to work independently, and think for yourself, balanced by
• the energy to research when you can't find the answer alone
• a committment to excellence in the result
• an interest in the implications of a requirement, not just a superficial resolution
• implicit trust that being taught to fish, rather than giving dinner, is a valuable gift, and shows that the giver trusts you

… what else?  What's on your list?