Yeah, who could need to know exactly how many items of a particular product they have in stock currently, or how much money a customer has in her account at the particular moment she wants to do a withdrawal? It's really hard to come up with any useful real world examples when this could be the case.
> What do you do when a transaction fails?
It depends on why the transaction fails and in which way. But sometimes it is really useful to make sure that when one account is debited, another one is credited at the same time.
Having access to the current state of the world is useful, having a log of what happened / how it got that way is essential. You've got to get the foundations right before you build a monumental edifice on top.