Interaction designers could improve thousands upon thousands of products, leaving engineers to deal with the areas of their interest and experience.
Engineers are professionals.
Each of those examples leads into a greater problem. Why door handles matter Donald Norman , a well-respected psychologist and human centered design advocate, introduced affordances to the world. Affordances are essentially the perceived properties of a thing, such as a door handle. Some door handles look like they should be pulled, because they have a shape which leads our brains to believe that is the best way to use the handle. Other handles look like they should be pushed, a feature often indicated by a bar spanning the width of the door.