I once ran into a dispute with a coworker who was a real piece of work, I had the displeasure of working with her for about five years. She was arguing a work related point with me where I was sure I was right, but she was equally sure she was right. It was actually quite an important subject of debate, something that greatly impacted the direction of teams, so it wasn't one of those arguments that you want to win for the sake of ego, the settlement of the argument had huge consequences one way or another.
If only we could have recovered an e-mail that was sent about 3 years prior, the whole matter could have been cleared up. In my favor.
Little did she know I have archived every work related e-mail thread I've ever participated in, going back to the early 90s.

She lost the argument.