One exists to prove to you that you do not know everything. The other exists to prove to you that they do.
A few months ago, this lady called with a problem with her HVAC system, could we please come look at it? Sure, we can fix anything, that's our story and we're sticking to it. So they send out a tech, who is confident in his ability to fix any heater or air conditioner. There, lo and behold was a weird looking part that left him scratching his head. It baffled everyone in the shop for a month. And everyone else too. Anyone who walked in was subject to be asked what the heck was this? They finally got a hold of the parent company and were informed that they were holding a squigalator, no there is not a replacement part, try this instead, just as calmly as if they were being informed that the sky was blue. For about three or four years this particular company created an additional part called a 'squigalator' that acted something like a valve (from what I understand). It only fits into one kind of system. Because the system is so old, never sold well, and pooped out pretty quickly, they simply stocked parts for a few years and then purged, and squigalators went quietly into the night. I am willing to bet most HVAC techs never once saw or heard of a squigalator.
Daddy used to swear he knew everything about HVAC. The squigalator says otherwise.
Last week, Mom went out to the utility room to take her shower. She tells me she kept hearing this mewing coming from someplace nearby, outside, and she thought it sounded like Lynxie. But all the cats are in Houdini-proof pens, so it couldn't have been one of hers. But she went outside anyway to see if it was a stray or if Lynxie has slipped out the door with her. No, she didn't see any stray, but she could hear this Lynxie-sound-alike a little louder now. So she went out into the yard to look around the house. The sound came from above. Lynxie! She was on the roof.
Mom used to swear she had those pens secure. Lynxie says otherwise.
Incidentally, a google search on 'squigalator' produces
this.