Used to say when you think something is very unlikely. For example...

A: I'm sure Simon got up really early today and has been working all day.

B:_______! You know very well that he was out partying all night.

Used instead of yes to emphasize that somebody has guessed something correctly.

You can use this idiom when you are very sure of a statement you are making.

We use this idiom if a particular event happens then your current forecast, and whatever
you had planned or expected, etc. will no longer apply.

To risk everything you have on an investment, a bet, etc.