books summary (business, investment books included)

Many books are published. Coupled with busy life, we often don’t have enough time to read enough books to gain new insights.

Learning new knowledge, gaining new insights are important. One of the "7 habits of highly effective peoples" is "sharpen the saw".

Is there a way we can learn the important concepts of books without reading whole books ?
Is there a more efficient way of gaining new insights ?
(Much like 80/20 rule: e.g read 20% of a book to gain 80% of its insights)

A friend of mine once told me there is this website called Business Summary.
website
It is a great treasure of books summary, investment and business books included.

You may wish to check it out. Previously I got the trial account which enables me to read (and download !) summaries of books for 2 days. The website will occasionally send book summaries to email account.

It may be more helpful if we know before-hand which are the good books worth reading (meaning "classics").