One of the hinges on our front screen door was coming off, the screws were coming loose from the wooden door jam. So I screwed it back on.

My wife and son then told me I "broke" the front door. I was confused, I thought I had fixed it

Turns out, with the door coming off the hinges, it wasn't closing properly, which meant it was ajar most of the time, so our dog could push it open with her body.

Now I'd fixed it, it closed properly all the time, so our dog started whining for someone to open the front screen door for her

So I loosened the screws, and hence "fixed" it by breaking it again

Absolutely, and you'll have all kinds of fixes for the symptoms throughout the project.

COBOL isn't hard, the tooling around it on old systems are a pain though.

Indeed, there may even be a whole lot of code that depends on it.