2/9 Empathy is the best yardstick
There are plenty of rules and principles to basic usability of applications or websites. But experience is important, and watching your test subjects is important, because nothing is set in stone. On a case by case basis, you never know what principle you'll be going against, what rule you'll have to break because it doesn't make sense to stick with them.
In those cases, what are you left with? The only thing that matters, which is your judgment. Not your judgment as an experienced designer - sure, that factors into it - but your judgment as a user. Nothing's better for the designer than having to use his own software. And not just using the software, but using the software under the same circumstances as everyone else who has to use it. In a practical sense, that can mean anything from performance goals to screen resolution.
That's empathy. Walk a little while in your users' shoes. A little bit of empathy for the user up front saves the need for sympathy later.
In those cases, what are you left with? The only thing that matters, which is your judgment. Not your judgment as an experienced designer - sure, that factors into it - but your judgment as a user. Nothing's better for the designer than having to use his own software. And not just using the software, but using the software under the same circumstances as everyone else who has to use it. In a practical sense, that can mean anything from performance goals to screen resolution.
That's empathy. Walk a little while in your users' shoes. A little bit of empathy for the user up front saves the need for sympathy later.