I think it's breadth and depth of experience - both in using software, and in writing/supporting it - that is the truly correlated variable. (EDIT: though, yes,

I think it's breadth and depth of experience - both in using software, and in writing/supporting it - that is the truly correlated variable. (EDIT: though, yes, you're right that introspection and thoughtfulness also help. Someone who's been through a hundred firefights and not learned from them will not think about those things - but also, an introspective and thoughtful person who hasn't experienced or heard of certain failure cases won't have easy references or checklists to call to mind)