Web designers are the worst people to have design a website.
Pretty controversial, but hear me out.
If you're designing as a career, chances are you're living and breathing design, using a range of website styles without a second thought.
That puts you in the 'savvy user' category, nothing phases you, it's simple, right?
Not for everyone. The world is built up of people with different levels of experience, different abilities and restrictions, and not everyone thinks the way you do.
Empathy is the highest value tool here. If you're not speaking with users, seeing things from their side, and making it work for them, then you're not designing the best product you can.
Forget balance, color sense, or other classic designer traits. Empathy is unrivalled as a skill a user interface designer should have. Walking in somebody else’s shoes (or seeing through their eyes may be a better metaphor), can be a temporary replacement for having a user/tester at hand.