Most important books

I am thinking to collect a list of books. Each of them should be an important one to read to help a person understand this world.

Why am I doing this? I found it is a pity to not to find a great book earlier. So the reason is that it is serving as a reading list for people, including myself.

Your contributions is highly appreciated. Please provide the following information.

1)Book Name and Author(with a link to Amazon or Barnes& Noble)
2)Why this book is important.

Ok, so let me start with this one
1) Name and Author(with Link)
Extraordinary Popular Delusions and the Madness of Crowds and Confusión de Confusiones by Martin Fridson

2) Why it is important?
"This is the most important book ever written about crowd psychology and, by extension, about financial markets..." -- Ron Insana, CNBC