Understanding MySQL Replication "fatal error 1236": "Replica has more GTIDs than the source has, using the source's SERVER_UUID"

This MySQL replication error — fatal error 1236 / Replica has more GTIDs than the source has, using the source's SERVER_UUID — shows the importance of thinking before acting. I am glad a non-DBA Colleague asked me about it, because if he had restarted replication, it would have caused a much bigger mess. Often, we are tempted — or pushed — to just restart things