The key is to align corporate growth with individual growth. If employees are growing faster than the company, then they will not be challenged and will leave.  If the company outgrows the employee, then finding the right role for that employee, whether inside or outside of your organization, is the right thing to do.  We invest a lot  in employee growth.  I call it a contract of employability.  For every quarter that you work at a company that I manage, I expect you to learn something new that is a sellable skill that makes you more employable.  In early stage companies there is not a contract of employment, but rather lots of uncertainty.  Through acquisition or failure, looking for a new role is just part of being in the tech community.  I want our employees to have a lot of new skills whenever that time comes.