While this is often true, I work for a company with some very aged computer systems and there are at least a few people I can think of; masters of the old ways, who are known to be essentially 1 of 1. The CEO may not know their name and expertise but the CIO on down definitely does.

The biggest injustice of being fired when you were very important, is that often no one even knows that your absence is responsible for the fact that a bunch of stuff is going wrong. Maybe your direct manager and coworkers will think “Oh, shouldn’t have fired them!”, but there’s no chance that upper management will be aware or hold anyone responsible for letting you go.

I was running a VBA macro I made in Excel at an old job that did the work of three people. I told my boss where to find my files when I left (shouldn’t have, I was young), but from what I hear he never bothered to look into my old work at all. They just hired three extra hands after I left. No one realized he cost the company $200,000+ a year or held him accountable.

ProTip: Offer your services back to them as a consultant for an exorbitant hourly rate. It isn't unusual to make three times what you would have made in a year, in just six months.

SOURCE: My firm has facilitated this for our clients' ex-employees – whom they fired to begin with – a number of times.

True, they won’t know that until I’m already gone. But I can sit happily at home knowing that in about a week or two, they are going to be wishing desperately that they hadn’t let me go