Could your position be filled by a lesser primate?
Could a properly-trained chimpanzee, or potentially even a gibbon or a capuchin monkey succeed at your job? Do you feel secure that they would not be promoted before you were? I feel comfortable making such comparisons between species of primates because I took a class in college called "Primates," which I got a C in. I bet you didn't know that the only thing standing between monkeys and your job is the folks at PETA, who think that placing animals in entry-level administrative jobs could lead to symptoms of boredom, indifference, and even disillusion.
The above photos compare myself and a chimpanzee in front of some sort of computing machine (no wise-cracks about who is who, thanks). Who appears more comfortable in the workplace? Notice the chimpanzee's relaxed manner as he sits at his typewriter. He approaches the day's work with confidence and patience, topped off with a zest to succeed. In contrast, note the overwhelming sense of frustration in my face as I yell at the uncooperative computer before me. Of special interest: that is not even a real computer I am sitting behind. It was one of those plastic ones they put on top of desks for sale at Office Depot to show you what a real office would look like if you bought that desk. I have become so accustomed to experiencing irritation and aggression at the hands of a disagreeable computer that it is now something of an immediate response.
So exactly how confident are you that you are irreplaceable? I'm not so sure we have that kind of comfort. After all, ambition is ambition, whether or not your diet consists mostly of bananas and live insects. They will start the same way we did; first maybe a work-study program, followed by an internship, eventually they will be working full-time with benefits in your office. Have you ever tried to make small talk with a monkey? Between you and me, they are insufferable.