Another reason for knowing 23 things...

Seth Godin writes...

As far as I can tell, assigning a textbook to your college class is academic malpractice. They are expensive. $50 is the low end, $200 is more typical. A textbook author in Toronto made enough money from his calculus textbook to afford a $20 million house. This is absurd on its face. There's no serious insight or leap in pedagogy involved in writing a standard textbook. That's what makes it standard. It's hard, but it shouldn't make you a millionaire.

Online Textbooks - http://www.flatworldknowledge.com/