Both my previous and current employer have some long-serving staff. One was incredibly effective because he effectively carried the entire oral history of the s

Both my previous and current employer have some long-serving staff. One was incredibly effective because he effectively carried the entire oral history of the software system; it would have been a massive loss if he'd ever quit for some reason. Not even a union position, just has to be a "normal" company doing the normal thing of selling a product and/or service to customers rather than a stockmarket rocketship or a consultancy bodyshop.