In my experience, (fellow) engineers conflate the importance of the work their doing and the importance of their role as their personal importance to the company. They think that because they build (part of) the product, the product can't be built without them but most engineers (and employees) are fairly replaceable. How many times has someone put in a two week notice and the company went out of business?

The only thing that's really irreplaceable in a company is creativity and personal skills, something engineers typically don't value.