If someone were to write code to their software fixing bugs, how and why can that break other code/features if it’s not meant for that? A common example are Nvidia drivers “breaking” or Microsoft patching one feature but breaking many, many other features.
If code is meant to be hyper specific, how can it affect any other feature?
Good programmers try to follow the DRY principle: Don’t Repeat Yourself. A lot of times you need to do the same actions over and over in different parts of a program, so you write a function to do that, then just repeatedly call the function. If you have to modify a function to fix a bug in one place it might change the input/output somewhere else unexpected.