delusions of grandeur--someone explain this to me

Okay, someone HAS to explain this one to me.  In the 20 years I have been with DH, virtually every job he has had he has described in the same way: he is the ONLY one there who knows anything, he is the only one who knows what's going on in the company, thank goodness they hired him because otherwise who knows what would have happened, no one else in the company has any clue...  You get the idea.  And yet, he has been fired twice in the past three years and it took him a solid year to find another job this time.  So how does that compute?  After both times he was fired, he wasn't so much mad about getting fired, he was upset because now the company was going to be in trouble without him and now could they not realize that he was the ONLY one there holding the company together?  HOW does someone actually think that about themselves?  I'm sorry, unless you are some brain surgeon who is truly the only person who can perform some particular procedure, we are all replaceable.  And furthermore, all of the companies he worked for/was fired from were doing fine before they brought him on board and continue to do fine without him (go figure).  This from a person who in our house cannot finish one darn project EVER no matter how many times I ask.  I understand having confidence and knowing you are good at your job--I have been teaching for 13 years and I am a really good teacher-I care  mightily about my students, my families love me, I have a lot of leadership roles in our school, the principal trusts me, BUT if I took a new job next fall, the school would not fall apart.  I am not the only good teacher out there for goodness sake.  So this morning I just about cried--DH started his new job December 15, so not even two weeks in and sure enough, this morning I got the speech about the last guy who did the job and how much he screwed it up so now DH has to go and undo and redo everything he did wrong.  I actually felt my eyes fill up and had to make some excuse and leave the room.  Are you kidding me?!?!?!  NO ONE likes to work for someone who has that "you poor stupid people thank god I've come to fix everything you have been doing wrong" attitude EVEN if it's true and I can assure you it's not or he wouldn't have gotten fired...twice.  What do others think of this?  What is the explanation for this wildly unrealistic view of oneself?  It's really hard to deal with/listen to because all of the REAL ACTUAL evidence suggests it is not the case but in his mind he is the savior of the facilities world and everyone else is just screwed that they cannot see that.  Help!!!