Sound it out: Do you "see" or "hear" words you have to spell?

I have an extraordinarily intelligent friend. Halfway through veterinary school, she's a hard worker, an avid reader, and scores highly on standardized and academic exams. She excels at what she does, and I've met few other people in life with her brand of outstanding dedication and commitment.

But there is one feature about her that is so strangely unexpected—so strikingly opposite her accomplishments—to the point where it's just comical.

She can't spell to save her life.

Now don't get me wrong. The spellcheck has saved me more times than not, and while I'm no Arvind Mahankali (13-year-old New York native who just won Thursday night's 2013 Scripps National Spelling Bee; seen above competing in 2011), I never had too much difficulty remembering how to spell words that I'd read. What do we know about spelling, and why are some of our most brilliant peers some of the greatest misspellers out there?