I noticed a lot of comments about documentation. I always documented everything, most colleagues thought too much. I found a lot of bugs that way.
My first app ran for 18 years without a single change. It increased the company’s share of the entire market by 20%. They had to run emulators of prior machines of prior machines for many layers to keep it running. IBM changed the characteristics of one data type and nobody understood the code enough to fix it.
I asked, “Didn’t they read the documentation?” It should have been an easy fix. They had lost it.
They finally bought a package to replace the app. The package was not as accurate.