people who see an unfamiliar UI and think "Oh no what the hell is this, I don't remember it! Panic, panic, panic!"
Or sometimes people see an unfamiliar UI, think "ugh---yet another drain on my time to figure this out", consider the value of what they are trying to do, and may decide it's not worth it. This is why I largely stopped using MS Office when the "ribbon" debuted. It seemed to me to be an arbitrary change to something that had been long familiar, and I decided "I really don't need Office anyway" and stopped using it.
Or sometimes people see an unfamiliar UI, think "ugh---yet another drain on my time to figure this out", consider the value of what they are trying to do, and may decide it's not worth it. This is why I largely stopped using MS Office when the "ribbon" debuted. It seemed to me to be an arbitrary change to something that had been long familiar, and I decided "I really don't need Office anyway" and stopped using it.