This is quite funny in a painful way. I identify on a few different vectors. I started my "professional" career in telecom. There I really did become an expert on some very small percentage of code. It was exhilarating to do patches in 286 assembler for an obscure language (CHILL). Now many years later, I work in NPD at one of the small divisions of a giant Medical device company. I wrote 90% of the legacy code. It is embedded and I have not needed to update any of it in 10 years. With changing management styles, the new push is to buy new products from smaller companies, and just to the required paperwork for regulatory approval.