Why Do Employees Really Leave? Seeking Insights for My HR Project on Attrition

The major factor threatening every organization today is attrition. I have selected that to be my project in a telecom company. I am pursuing my PGDM specialization in HR. I would like to have inputs from my fellow HR professionals on "Why an employee leaves an organization?" For example, lack of a good salary, boss, job satisfaction, recognition, etc.

Your input would be appreciated.

Regards,
Priscilla.

This is Uma Kakileti, working on my project in a reputed Pharma company. I am focusing on "Why Attrition happens and how my company is trying to Retain the employees." Can anyone help by providing the complete format of this project along with content?