You are Definitely Underpaying
You must have hired your employee at a competitive market rate and would be giving him or her consistent incentives. But, you need to understand that every person grows as professional as the time passes and your payment rates should be consistent with his or her skills.
You Must Be A Jerk
Employees want their bosses to pave way for their progression and empowerment, but if you are someone who likes to micromanage, look down and condescend, rest assured your employees definitely consider you as a jerk and wouldn't think twice before leaving, should they get another opportunity.
Don’t Make Your Dream Their Nightmare
Being the boss or a manager, you would definitely consider the project your baby and would be willing to burn the midnight oil to make it click. What you need to understand though, is that for your employees, it may be important, but not more so than their personal lives. You curiosity and eagerness to get things done quickly may be the driving force behind their desire to leave.
LinkedIn Will Help You Get A Clue
While it may not be ethical to keep a constant check on the LinkedIn profiles of your employees, checking it from time to time may prove helpful to understand their mindset. If any employee has been very active on the network, it is a clear cut sign that he or she is in search of an alternate option.