In Scott Shenker's talk about SDN, he recounts a 1985 visit of Don Norman to Xerox PARC.

At start of his talk on UI design he asks:
“Who in the audience drives a stick shift?”
After most of the audience raises their hands, he looks sternly out over the crowd and says:
“None of you should ever design a user interface."

Moral: Engineers will look to optimize rather than take a penalty for ease of use. Engineers need to learn to resist that instinct.