The 80/20 Principle (1999)

The 80/20 Principle by Richard Koch is a book to help you understand that both life and business are really in an unbalanced state. 20% of your work leads to 80% of your outcome. 20% of your customers bring 80% of your profits.  

The better you understand the principle, the better you can find an efficient way to gain your success. It's essential to work smarter than harder. 

On the other hand, you have to admit that you can't work with everyone and work on everything. Choosing the 20% most valuable customers, spending time with the 20% of people who care about you, and working on the 20% of tasks that lead to 80% of the outcome. 

The 80/20 rule a must-know principle for any leader. ​