* You are dependent on your employer for your work visa; * You are dependent on your employer for your health insurance (US-specific problem); * You have don't have much experience in industry and thus will not easily be able to find a similar job; * You don't have enough savings to be able to be unemployed for a period of time while you find another job (doubly so if you have dependents or you have a non-compete agreement which would make you unemployable for a significant amount of time); * You have a criminal record that makes hiring far more difficult; or * There are few competitors in the space where you have expertise (or the few competitors you do have wouldn't hire you for one reason or another).

There is a very large number of people which would fall under at least one of the above points.