If you own a business, check your business culture: How does your business feel about people who leave the team to take a different job? What about people who leave your business to start their own business? Are they your team alumni? Do you wish them well? Do you take pride in their new successes?
Of course ongoing businesses generate ex-employees for lots of different reasons. People move on, get better jobs, and change. Teams break up. People evolve and needs evolve.
Ask yourself this: Are ex-employees more likely to be enemies or friends of the business? Do you see a trend? What does this tell you about your management style?