I agree with AnthonyLar1. They have "Let's hope not.", as the default answer but I think that should be used with an exclamation.
Depends on how you use it. it can be either depressing or really depressing .
Chrisbaldo1: it's just the way italians say that. A native Italian would ask: Why doesn't English need to include "of". There's no good answer. That's simply the way it's expressed. Let me add, try to get away from the idea that 1 language will translate into another word for word or express an idea in the same number and kind of words. That's simply not how languages work.
Pensiamo di sì, in fatto crediamo di sì e, veramente, sappiamo di sī! ; )