Any investment account can be frozen as well as bank accounts in extreme emergencies.
IMHO the secret isn't the amount of money you save, but how low you can get your Dependecy rate. If it only takes $2K to cover all your monthly expenses, then $24K covers a year. But if your Dependency rate is just $500, then three years is only $18K. And yes it is possible to get a Dependency rate very low. But it takes years of work, no debt and active ways to eliminate expenses.