An irony of facebook's situation.
Sheryl got her MBA at Harvard. One of the most famous cases (Extra Strength Tylenol) in one of the most famous classes (Business History) she took: in 1982, someone put cyanide in Extra Strength Tylenol capsules and killed 7 people in Chicago.
And if ever you want to see the difference between school work and real work, it's right here. Real work is harder.