My friend and coauthor Susan Fenner sent me an email with the subject line "You're amazing!"
We exchanged many emails after that, and each time she replied, I received yet another email with the subject line "Re: You're amazing!" It was quite a pleasant experience.
Then it occured to me that Susan was receiving emails with the same subject line. It seems I had discovered another application of "You reap what you sow." What goes around comes around. In this case, it's a good thing.
I'm more conscious of subject lines now.