[chc]

I have a better grasp of the English language than the average college graduate, but I still make stupid errors even in the comfortable environment of a text editor. I might leave an article out, or I might miss a period, or I might write a homophone even though I know the correct spelling. As an editor, I've worked with a lot of professional writers — to a man, they all made mistakes as well. This is why I proofread anything important.

And that's under ideal conditions! Writing code on a whiteboard is so far from ideal for most people that keeping your variable names consistent is a challenge — balancing parentheses and brackets and keeping track of little dots is outright grueling, and doing all this during a job interview is enough to make even very competent programmers choke.