Worst day, but has a happy ending:
I was working on a team that provided an important library. While the library was theoretically generic, we really had one client within the company and they had a lot of weight within the company.
So one day we get assigned a high severity issue about how our library isn't working and it's showing up at the top of the stacktrace.
We had made some recent changes to the library (this clouded my judgment) but we had thoroughly tested them.
I spent all day working with the build they had provided me and there were all kinds of things wrong with how our library was working. I started freaking out and it didn't help that to get my dev environment to match their build version took a long time.
At this point I had manager after manager (going further up the chain) coming by my desk and messaging me for an update ASAP.
Long story short: I found that they had pulled a seemingly completely random old version from our library! So of course nothing new was working right and why "OurLibrary" was showing up in the stacktrace!
I had spent the whole time assuming it was our library and that they had the latest commit since they were the first to point the finger. I'd been in IT long enough to not take those assumptions as given but with the heat coming from managers I lost sight of that.
Solution: slam the ticket back to their team and tell them that they need to always merge from the tip of our release branch.
Moral of the story: Don't Panic. Verify all assumptions.
On the same team, I also had the pleasure of flying out on a red-eye to a client for no other reason that to just make people feel better by "having a dev on-site."
Needless to say, I left.
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