Three user interfaces (UIs) go to a pub. The first one orders a drink, then several more. A couple of hours later, it asks for the bill and leaves the pub drunk. The second UI orders a drink, pays for it up front, orders another drink, pays for it and so on, and in a couple of hours leaves the pub drunk. The third UI exits the pub already drunk immediately after going in — it knows how the pubs work and is efficient enough not to lose time. Have you heard of this third one? It is called an "optimistic UI."