Mistakes happen, and they can be hard to find afterwards…
I learned this lesson from my mentor, Roberto Percuoco. We had a session that we were working on for a client, and he wanted us to add in another track that he had recorded. At some point, one of us accidentally raised the send to a delay channel without realizing it, screwing up the entire mix. We listened to the exported track, noticed something was off, but couldn’t find WHAT the problem was.
Good thing we had the previous version still.
We didn’t realize what had happened until we loaded the previous version of the track. We redid the mixing session (adding just the track that he wanted) and wrapped up everything. If we didn’t have that previous track, God knows when we would have figured out what was wrong.