"I approached the start of college in utter denial of the fact that I'd been in any movies whatsoever," the 21-year-old writes in an essay for the February issue of YM magazine.
"I went to class in my pajamas like everyone else and insisted to my classmates that I was just another student."
But Stiles said she learned that it didn't matter how she behaved; people were going to have preconceived notions about her, and she just had to be herself.
Since she's been at Columbia, Stiles has appeared in movies including "State and Main," "Save the Last Dance," "O" and "The Business of Strangers." Her latest, "A Guy Thing," comes out Jan. 17.