Usability testing helps you find the problems
And that's a pretty amazing thing, because after staring at your design for hours, it's pretty tough to imagine what it will look like to someone who is seeing it for the first time. Usability testing allows you to see how your design might be parsed, interpretted, and confused by people who don't think like you.
That's invaluable.
But that's pretty much it.
It doesn't tell you the solution to the problems, It doesn't tell you whether people really even want the thing you're testing, And it certainly doesn't tell you that the million people who visit your site will all agree with the opinion of participant #4
So don't let me catch you saying:
“That girl from the afternoon session really liked
option A, which was, you know, our idea, so let's go with that.” 
Thehandful ofindividualsyou observe
aren't
there
to be
a simple
random
sample
of your site's visitors
They're there to help you find the problems
