There was a place I worked where I was responsible for all of the software builds and releases. I was brought in to help them because they were about to lose a major contract. They had 1 month until they had to demonstrate considerable improvements to the customer. If not, the poorly written contract would allow the customer to walk away without penalty, not even any progress payments. The problem I was specifically working on was that their build process was so messed up that it took about a week to get a working build completed. They knew that they would need many more than just 4 builds in that month in order to get all their testing done. I dug in, and pretty quickly we were able to do multiple builds per day. They managed to make enough fixes in the code to impress the customer and keep the contract. There were a lot of other improvements and updates and things were humming along well. At some point I scheduled a 2 week vacation, and pointed out to management that no one else knew how to do my job. Sure, there was documentation, but there were a lot of tricky nuances that wouldn’t be obvious to someone without some experience - this was not an entry-level job! Finally about 2 weeks before my vacation, they give me a new hire college grad to train. I only got him about half time though, so I basically only was able to train him how to do things if everything worked. I didn’t really have time to teach him all the intricate details, only the big picture. I went on vacation, and everything went smoothly. After I returned, they moved him back full time to software development. A few months later, layoffs happened, and I was one that got let go. A few months after that (got a much better job, more interesting and better pay), I had lunch with a former colleague. They told me that the other guy had failed to produce new software builds for about a month after my departure. They told me a bit about the problems they were seeing, and after listening for about 2 minutes, I said it sounds like they forgot to do this one particular step. That’s exactly what happened. Much of their work had ground to a halt for a month because management had thought that a half-trained new hire could replace my years of experience in that area. That was very satisfying