[nekusar]

No YOU may not have changed anything. Your colleagues might have. The system might have. The network might have. Windows/Linux updates might have.

Many of those are automated and usually escape proper review. And they can be minor or catastrophic.

I always try to look at "what changed that causes this failure?"

And do so blamelessly. Pointing fingers only gets disdain and blame.

[not2b]

In many cases, I found that when colleagues said "we didn't change anything" they mean "we didn't change anything relevant" which winds up meaning "we didn't change anything we think could be relevant to this issue" and then "whoops, turns out it was relevant after all".