Gershbein: In the last 10 years, we designed new systems for usability. Now complexity is so ubiquitous -- every design team is creating a new world for themselves. Every system is about figuring things out from scratch. There’s no core set of references to use.
Rebaudengo: How much do we want it to be simple vs. letting the person get pleasure from discovering and learning to master the tool? Some tools are good because they are hard to use -- a guitar is never going to be easy to use, but it’s very powerful.
Gershbein: Any number of inputs can go into a design project. For a digital UI for a car radio, we’re thinking about previous products, the gestures or inputs, what competitors are doing, what the brand represents, plus the end user. It’s not an easy tradeoff, but as a designer you have to look at that entire system of variables.
Rebaudengo: You have to ask, “How much can I change without losing all of the users in the system?” Some people can adapt, but there is also the harsh reality of a business losing clients with every change that you do.
Gershbein: The nature of design is making things better. That’s what innovation is. But the design side has not caught up with how prolific we are in creating things like interfaces and interactive experiences. It’s a double-edged sword.
This story is from the June 16, 2014 issue of Fortune.