I think in many cases people over-estimate their worth. Where I work I am the only real developer. I wrote and maintain all the products.
I learned this lesson the hard way, long ago, in exactly that same situation -- it took two times -- by attempting to use leverage I didn't actually have but believed I did.
I hope most people are less dense than I was (hopefully "was" is the right word there), because no matter what percentage of the work you do or how deep and unique your knowledge of a system is, you can be replaced. It may not be easy or quick, but if you make yourself a nuisance, get on someone's bad side, or any of myriad things in and out of your control, you can and will end up on the chopping block, wondering what just happened.
I learned this lesson the hard way, long ago, in exactly that same situation -- it took two times -- by attempting to use leverage I didn't actually have but believed I did.
I hope most people are less dense than I was (hopefully "was" is the right word there), because no matter what percentage of the work you do or how deep and unique your knowledge of a system is, you can be replaced. It may not be easy or quick, but if you make yourself a nuisance, get on someone's bad side, or any of myriad things in and out of your control, you can and will end up on the chopping block, wondering what just happened.