Human communications are more naunced than DB transactions. If I forget to mention something important I send a new message rather than editing the already sent one, to make sure I catch their attention. Edits can go unnoticed. Imagine this scenario:

[12:00 / sent] Sell the house.

[12:05 / failed] Please feed the baby.

[12:06 / sent] Oh and the cat too.

Now the receiver's going to sell my cat [example inspired by The Art of Multiprocessor Programming].