On a related note: I just ran across this article from the Neilsen/Norman Group on usability:
Summary:Across 33 rich countries, only 5% of the population has high computer-related abilities, and only a third of people can complete medium-complexity tasks.
One of usability’s most hard-earned lessons is that you are not the user. This is why it’s a disaster to guess at the users’ needs. Since designers are so different from the majority of the target audience, it’s not just irrelevant what you like or what you think is easy to use — it’s often misleading to rely on such personal preferences.
For sure, anybody who works on a design project will have a more accurate and detailed mental model of the user interface than an outsider. If you target a broad consumer audience, you will also have a higher IQ than your average user, higher literacy levels, and, most likely, you’ll be younger and experience less age-driven degradation of your abilities than many of your users.
There is one more difference between you and the average user that’s even more damaging to your ability to predict what will be a good user interface: skills in using computers, the Internet, and technology in general. Anybody who’s on a web-design team or other user experience project is a veritable supergeek compared with the average population. This not just true for the developers. Even the less-technical team members are only “less-technical” in comparison with the engineers. They still have much stronger technical skills than most normal people.
This is a bit "dated" at 2016, but I think not so much as to not still be relevant.
Note: If this post is a bit too broad for discussion here then please feel fee to fork.