Like I mentioned, I just get flustered when people are watching me, or want me to speak my though process aloud.
Those skills, (being able to code complex problems when people are watching) have never been a requirement of any job I've seen so I've come out of many interviews feeling that they got an inaccurate picture of my skills.
With some preparation, you can transform the problem from one that may not be part of your job (solving completely new problems in front of an audience) to one that certainly will - explaining your solution clearly to an audience.
If you try hard enough, you can be familiar with likely interview questions and then the problem is how best to present your solution, which is an important skill, and one worth practicing.
Yeah, I guess it's different with people I know. And to already be familiar with the problem helps too.
But to solve something say from project Euler on a whiteboard in front of three strangers and talk about my thought process at the same time, that's hard.
why not on a whiteboard?