Your problem is when someone you have a good relationship with is seduced by something hotter and sexier.
If an employee is seduced by an offer that doesn't work out - they can (and have) come back and can bring back what they learned.
One of the thing that I learned from such exits an re-entryies is that money is not always the best motivator - I used to run really lean to have a high payroll. Now I run lean to provide a good work environment - I can now fire bad companies that don't respect my employees.
It's great to hear someone articulating that point on HN. There is too often a constant stream of suggestions to the effect employees are a form of chattel.
All this analogy implies is that an employee can be seduced by a newer, trendier, higher salary startup.
Stop forcing your preconceived opinions and assumptions down my throat.