Designer != User

 "Designers are not users." Jakob Nielsen.

  "A design isn’t finished until somebody is using it." Brenda Laurel.

 "The user’s time is more valuable than ours. Respect it. Good UI design is humble.” Jono DiCarlo.

When designing, there is a strong tendency to revert to a line of thinking like

• 'what would I like it to look like' or 
• 'how would I expect it to work'.  

But, of course, it's most often it's the case that you're not the user! As designers, unless we have actual users on-site, we're often forced to make many assumptions about how aspects of our design will meet user expectations.  Our unvalidated design assumptions can be wrong in two divergent ways. 

We can assume that a particular design will cause problems with users. As designers, we sometimes ask far too many questions and therefore over think a design.  I run into this problem often. I think things are more complicated than they actually are.  There was a study (sorry, I don't have the reference) that looked at the accuracy of designers' prediction of usability issues vs. what actually happens when the design is tested.  The result was astounding. Something like 75% of design points designers felt would be usability problems were not born out in testing with real users.

The opposite is also often true.  How often have you been totally surprised when user after user stumbles over a part of your design that you were certain was fool-proof?      

So what to do?

• create personae for the various potential user types
• Recognize and list the assumptions you're making in your design
• recruit test subject that match these personae 
• talk to a few of those users, try to understand  their mental model of the problem space, and keep their mental model (not yours) in mind when designing
• test, test, test -- ensure your assumptions are validated or refuted through user testing  
• Lose your ego.  Finding your design assumptions are incorrect is par for the course