It depends on where you are. Where I work, were I to get fired, I would get a minimum of 3 month's pay, and they would have to show very clear cause. Realistically, if the company wanted to get rid of me, they'd have to negotiate, and there's a good chance I would walk out with somewhere between 6 months and a year's salary.

If you run your own business, it can be hard to work up to that level of reserve.