Code is extremely evil because you can accidently write ++a instead of a++ and create a bug so severe and so hidden you bring down the whole company.

I work at a company that does payroll software. Its not atypical for me to spend an entire week to write one singular line of code. Because in order to write that line and be confident it's correct, will always be correct, and cannot have any side effects, I have to read and understand so much other code.

The older the codebase is, the worse it gets. The larger the codebase is, the worse it gets. The more valuable your customers are, the worse it gets. That's why free consumer software is riddled with bugs and nobody cares.