Use automation to prevent bugs from re-occurring.
One of the most frustrating bugs you can see in a production system is one that was fixed previously. A bug that was already fixed once. For various reasons, bugs can reappear. Perhaps some old code gets reverted, or perhaps a developer repeats someone else’s mistake. In any case, people are going to be upset that this bug, which was supposedly fixed, is now back again to haunt the system.
This is why it is important for every bug to get covered by an automatic test. This includes any bugs found through manual testing. If you have a robust suite of automatic tests, it can go a long way towards preventing these bugs from returning.
Never let a manual tester see the same bug twice. Put your robots to work.