"Unfortunately, schools like this don't exist for every kid," she said. "You are blessed."
The first lady told graduates that failure may be a part of their college lives and careers, and that how they respond to any pitfalls will define them.
"That's when you find out what you're really made of in those hard times," she said. "But you can only do that if you're willing to put yourself in a position where you might fail."
Overcoming adversity has been the hallmark of many great people, she said.
"Oprah was demoted from her first job as a news anchor, and now she doesn't even need a last name," she said of media giant Oprah Winfrey. "And then there's this guy Barack Obama ... he lost his first race for Congress, and now he gets to call himself my husband."
Mrs. Obama later presented graduate diplomas on stage and posed for photos with graduates.
"We didn't know we would get to hug her," said graduate Natey Kinzounza, 18. "She's got a great sense of humor. She's like my mom, she's just a very real person."