foo.swift

func mightFail() -> Bool? { // Return type of this is actually Optional(Bool) because of the ?
  return nil
}

func main() {
  guard let result = mightFail() else { // This unwraps the Optional(Bool)
    print("lol get rekt")
    return
  }
  
  print("Result was: \(result == true)") // No compiler error about `result`, it is not possible for it to be nil here
}

Other variant is:

func mightFail() -> Bool? {
  return nil
}

func main() {
  if let result = mightFail() {
    print("Result was \(result == true)") // In this context, `result` has been unwrapped to Bool
  }
}

Or if you hate yourself:

func mightFail() -> Bool? {
  return nil
}

func main() {
  let result = mightFail()
  print("Result was \(result! == true)") // Optional(Bool) `result` is force-unwrapped with the !. Runtime crash if it's nil.
}