What are the basic attributes of a design Engineer ?
Well i guess you should study the introductory chapter in mechanical machine design books. They can say a lot better than others.
- Selection of Materials, Surface continuity, Size of part, GD&T, Cost of Production, and above all Safety of Operation etc.
Imagination, perception, looking around and very wide abilty for searching for knowledge. It's often forgoten that maybe your task is solved by someone else - see and search patent bases.
The Mother Nature was solved a most of our problems but we must find it.