What does it mean" The question is not if but when."? please give me context example.?

Question

I also need context example and meaning of this" not if, but when"

please with complete explanation and example

Answer 1

Suppose you say: "If we go on vacation this year, ... " and your friend interrupts you and says: "Not if, but when!".

Your friend then means that the question is not WHETHER you will go on vacation, because it is certain that you will go. The real question is WHEN you will go, because you still don't know if it's going to be a summer vacation or a winter vacation (for example).